Diable seems really persistent in this Nex campaign I've been playing. They will sometimes reengage when they only have freighters or tankers left. For special fleets like invasions or expeditions, even if they decide to disengage after losing a fight and having no combat ships, they might continue on the mission with just the tankers and freighters left.
Also, I recently fought a station that had a small fleet with it. I destroyed the station and most of the fleet in the first battle. Afterwards, a single freighter + draft wanted to fight my fleet still. The first time, they only sent out the draft. The second time only the freighter. The third time, they sent the draft out again. After that third time, the draft was out of CR but was still alive somehow.
Finally, for some reason, Diable generates its 3 normal systems in a random generated sector. This leads to them having twice as many colonies to start with as anyone else generally and then stomping everyone.