I don't know how long the 770's will last... but I'd bet they'll last a lot longer than folks want to give them credit for...
The truth is, most hunting rifles will digest about 20 to 40 rounds per YEAR... for their whole life... likely, even less than that for many.
I think it's pretty amazing that the 770 can shoot this well, at its price point. Ruger Americans are doing the same; they're shooting lights out, on average...
I think Remington knew that no one would seriously rebarrel the 770, so there was no need in making it a "take apart" design... your son will probably end up giving it to his son one day, with around 300 rounds total down the tube... and it'll serve for another generation...
...and then some...
Dan