When using Glorfindel ( https://ringsdb.com/card/12006 ) as my MotK hero, when he dies, can i just buy him back as an ally from discard? I suspect yes, but it's weird.

Glorfindel coming back from the dead is canonical, I believe he's the only elf known to have appeared in Middle Earth in two lifetimes.

You can also Stand and Fight any other MotK target once they enter your discard pile.

And then Sword-thain them

for good measure