One roach infestation bankrupted me from over $2,500 (which I'd been saving for hours) to a fraction of that. I was also behind the count in water treatment, I figured I'd rush it to break even, it failed (like it always does with me-it was at 32%/33% incident), roach infestation wiped out everybody in the water treatment plant and nearly everybody is irradiated to half of their health. Population is 21 people (down to 16, I let 5 go), so I'm kind of starting out. Is it game over? And if not, how do I come back? I'm broke and water treatment generates very slowly, everybody is irradiated and I keep getting attacked with no stimpacks or radaways.

So here is what you can do. Click on a few rooms not in use and go to upgrade. You can then sell that room to make a few caps back. Best to sell off storage rooms first as they aren't needed at this point and are just a waste of power. Next thing you can do is move what dwellers you do have around. Look at the special and move the ones that have at least 2 P and move them into the water room and try to get that fixed first. They may not be the fastest so it's a good idea to quit to menu. This will do two things one give dwellers time to create more supplies, two prevent bad events from creating a chain reaction. After a bit of waiting load the game gather everything and go back to the menu. Keep doing this till you get the levels back up. If worst come to worst you may have to just not revive the ones that have low stats and just sell off any low tier equipment you have. It's not much but it will help in the long run.

If all else fails and nothing else works then it is time to make a new vault.

If you have to make a new vault you way want to try some of the following tips.

1) Don't upgrade rooms till everyone has a decent weapon that deals good damage. Instead expand rooms as long as you have enough dwellers to cover the extra space. Doing this will prevent radroaches from being overpowered do to the fact that they get stronger when the room is upgraded.

2) Breed dwellers at a slow rate. Never have more then two babies at a time. This time this will help prevent the over usage of food and water.

3) When sending out more then one dweller to the waste send them out all at the same time this way the vault door doesn't keep opening and closing. This will lower Raider attack rates. Do the same thing when you bring the explorers back.

4) Don't sit around watching the timers it's best to load the game gather everything and quit to menu. Build when needed and you can leave dwellers alone in the living area so they can make a baby then move them back when you load again. I find it best to check back every 3-4 hours. This way everything should be really to gather, explorer's should have something at this point, and kids should be grown up ready to work.

Most probably it is. Remember that most Vaults in Fallout universe were subject of experimentation, so you must actually get lucky to make a "control vault".

Stil.l, you may have several chances to survive, but at a heavy cost:

Problem: As you say, resources generate slower, probably because you have size 2-3, heavily upgraded rooms, and you cannot cope anymore with the SPECIAL amount those rooms require to generate resources at a decent pace.

In order of preferences, I'd say (you're free to mix and match, specially #1 and #2):

Solution #1: While it takes some time... focus on rushes instead of normal resource generation. Cap a room with your most proficient SPECIAL dwellers, armd them with everything you have left (in case of further infestation), rush that room, then move them to the next one and repeat to (hopefully) generate resources, then relocate them somewhat evenly and disconnect, wait some minutes (or do the clock-trick) for the rush failure chance to drop to it's minimum, return to the game and rush again. This should place you in the green or totally destroy you If you cannot handle the hazard of another failure. The LESS time you spend in the game, the better, and rushes will slowly net you caps for that heavily needed medbay or lab, if you haven't any.

If you cannot build the medbay and lab because of your dweller amount, while you're doing the rushes send two dwellers to the dorms tfor some whooing; just remember to disconnect the moment you get your female pregnant, and keep track of time (you need 3h to give birth, then another 3h for the kid to grow up to advlthood). You do NOT want to stay in-game because a raider attack will probably finish you off, but you're not prone to attacks when disconnected. Once you have built a basic medbay and lab, rush them the same way you do with the other rooms, this should stabilize your dwellers.

Solution #2: Send several of your dwellers to the wasteland (even without protection). Wanderers do NOT consume resources, so your vault resources will drain slower; just keep an eye on them from time to time since you don't want more deaths. Hopefully, they'll get a couple of items (specially weapons) that may help on rebuilding the vault.

Check the Fallout Shelter Efficiency Data spreadsheet; there's a lv1 "nvde wanderer" experiment there that lasted for about 2h, think of the levels you have on your wanderers, and that they'll be at half-life to give you an idea on how much your's will last.

Solution #3: Depending on the money you have left ... you might sell your most expensive rooms and the ones you dont have use for (empty rooms consume energy, but you say that's still not your issue), and rebuild lower version ones that you can work with and generate resources at a decent pace. It's extremely expensive but still a decent choice.