So I accidentally stole something while I was in the hotel and that made everyone start shooting at me, I was still new to the game, so I killed everyone that was shooting at me. Turns out the people I killed people are permanently dead. Is there anyway to fix this? There were people in there I'd like to talk to, thanks.

On pc? If their bodies are still there open the console, click the body, type resurrect, hit enter. Try that.

For the future you might want to consider putting your gun away if a friendly npc attacks you for stealing, that might make them stop and forgive you.

Edit:Misunderstood, didn't realise you had already killed them all.

Try reloading to a slightly earlier save if you have one, messing with console commands isn't always the best way of doing things like that, it can have unforseen side effects.

If this every happens again, you can just run away, wait for 72 hours, and the area should reset.

Unfortunately I did this early on in the game, then I left and carried on thinking it would come back to normal next time I went there. Now I've completed the game and everyone is still dead. I'm on PS4 so I can't even use the console like PC players can :/

Then you have to do it on your next play through.

Why did you assume they would come back to life? There are no necromancers hidden in the hotel.