While this topic ~has~ been discussed to death already..... well, what else are we gonna do?
One thing I haven't seen mentioned before is this ---- if your spouse and/or child leave (or are taken from) the vault before your character.... why ~wasn't~ your character also taken out at that time? If the spouse and kid wake up through automated systems or some glitch and find you still frozen, would they wander out in the wastes or would they settle down in the general area and wait for the PC or try to figure out a way to un-freeze the PC?
I suppose at some point they might "give up" on the PC and go out to live their lives (or they could always be abducted by raiders five years later, having still not figured out how to free the PC)....
If the spouse/child were taken by some external agency, I still have to wonder why they didn't take the PC, too. It almost requires that the PC be somehow inaccessible, like your stasis tube fell through a breach in the floor to a lower level or something. If all the stasis tubes were together --- and they likely would be if the PC had any choice in the matter --- then I can't see why the spouse and child would be taken out and ~not~ the PC.
If the PC is somehow separated from the others AFTER they're put in stasis, it could well be that when the spouse/child are woken (automatically or by others) they might think that ~they~ are the sole survivors, and that the PC is dead ---- a vault collapse apparently destroying the PC's stasis tube or something. Likewise, if an external force were responsible, the only reason I can think to leave the PC behind is that don't ~find~ the PC as readily as the others are found and assume they have possession of all the survivors with just the spouse and child.
If the vault destruction is more widespread than just enough to obscure the PC's stasis chamber, then it could very well be that the spouse. child ~and~ PC each think they are the Sole Survivor of the Vault.
Mom: "I'm the sole survivor."
Shaun: "No, I'm the sole survivor!"
Dad: "No ~I'm~ the sole survivor!"
Institute Scientist, pinching bridge of nose, "No, no, you're ALL survivors of the Vault!"
They've almost painted themselves into a corner with the way they've done this ----- if the PC is frozen for 200 years, then wakes up "in the future", it looks like the only real motivating factor ~would~ be to find the spouse and child. The only way that the PC would be interested in some other plot would be if the spouse and child are clearly dead. In ~that~ case, the PC could be drawn into whatever plot they wanted. And frankly, if I woke up 200 years in the future and found out my family were dead, I'm not sure what kind of plot ~would~ motivate me to go out and explore and shoot monsters and such... why ~would~ I? Why would I care about this foreign, strange land that USED to be my home but now is a ruin?