This doesn't serve as evidence that the PA would be willing to arrest Hamas members.

The PA routinely arrests Hamas members. On the daily. Locks them up or hands them over to Israel to lock them up for years. Isn't that already evidence?

Fatah and Hamas have engaged in open combat regularly.

Willingness isn't really in question. Ability to do so is, though.

To be fair, the GP comment asked what one thinks about the possibility, and the parent comment provided some limited grounding. It’s a bit difficult to provide concrete evidence for a hypothetical.

ICC issued a warrant for very dead Muhammad Deif.