No thats the problem you face when you have post MQ free roaming in a story related game.
Your focusing too much on the problems that the games have now. And not about the what IF's for future titles. Fallout 3 OR NV wouldn't work with post MQ gameplay because they Are FALLOUT 3 AND NEW VEGAS.
Now if Fallout 4 had a brilliant story, and let you experience the consequences and impacts you've made in the MQ without compromising,any story lines or screwing over fans of the BoS or Enclave or anything like that. Would you get mad? Obviously you wouldn't you'd probably enjoy it and be satisfied. I'm not contesting the endings of NV and FALLOUT 3. I'm contesting the future of series which was the whole point of this thread in the first place. I've pretty much had everything to say.
And before you start the whole "HE HAS AN OPINION, HE MUST BE NEW TO FALLOUT!!!!!!!!!!111oneoneone"
I've played Wasteland on my fathers apple as a child, and loved it.