The collector would likely attempt to avoid fighting since he prefers not to be enemies with beings of equal or similar power
However
The collector has hundreds of universes at his disposal, he could easily trap zanthor in one of these universes and destroy it with him inside of things don't go to plan
I don't think you understand, because Zanthor can open portals to other universes so he could easily escape one. Also he has Bill Ciphers eye it itself contains a lot of power. Plus he has cupead's 1st super which in-game can kill the devil himself
That would create a paradox
Because the multiverse is infinite the newly formed universe would be infinitely large
There's a reason that universes are separate
Most universes apply to different laws of physics meaning many parts of the newly formed universe would just be universe sized black holes which since there are infinite of these universes would destroy everything in the newly formed universe
Which would be one way to defeat the collector but he would kill himself in the process
his weakness is not time because he could just pull something from another multiverse entirely to stop it, everything has at least one weakness, I will not tell you Zanthor's
And the reason Zanthor wouldn't negotiate with the Collector is because Zanthor seeks power, and can drain it from any kind of living organism, imena like, how do you think he got so much power