But it can if, like FO2, the freeplay mode essentially ignores what's gone in the ending and plonks you back in the world as it was before the final mission. Nothing even really needs to change in the world. Story mode is finished, now you get to play freeplay. Really, I think that's all that needed to be done to appease the peeps who want to play and play and play with the same character.
No, but they could easily design the end of final quest in the main questline to involve plopping you back into the gameworld with no changes, especially since not being able to play after the ending is one of the greatest complaints around here.
Then the basic logic is to keep a save before the battle and/or say no when the popup tell ya there no way back.
Like I say, the ending emphasizes there is so has much changes within a short time after the battle. Just popping the PC back into the game world would not make any sense nor there any "accomplishment" is felt because nothing changes overall if it is done this way.