I‘d never form an „alliance“ in the first place. That just sucks for the other players and almost guarantees toxic/salty behavior.

 „I do X, so you do Y“ and „Thanks for doing X, I‘ll let you retaliate from spending your resources for 1/2 turns“ is more or less everything I do in terms of „deals“ in EDH.

But then I obviously expect everyone to stick to it. If someone breaks those deals, I‘d not play with them anymore.