Dude I get it. And IMO you had a total fluke failure based on info you gave. If it makes u feel better I had 2 rear ends blow up on the same truck, 2 weeks apart, both times on the road with h trailer hundreds of miles from home. And the truck was Brand New!!
First don't freak out about the big ticket things like engine and trans. Yes older, high miles = anything is possible, but typically there are symptoms before all out failure and if you're going to spend thousands on rebuilding serviceable major components for peace of mind then spend that $ on a newer truck and let this one be someone else's baby.
That said I do think it's worth replacing what's likely newer the end of its service life for ancillary components.
