Hello, I'd like to ask for a little clarification. Let's say if I, as I'm in an rdf, I would state to the rest of the party I would play and clear the dungeon up to the first boss kill and I would tell them I would be leaving the dungeon with deserter as soon as the boss is dead and do indeed take the deserter debuff, would that be considered disrupting gameplay?
Probably up to GM interpretation of the whole scenario, not just what you're saying.
Going simply by your description, no, it would be fine. But how does the rest of the group reacts to it? Are they fine with it? Do they say that isn't acceptable and you have to leave? Do you leave if they say that and take the debuff or try to make a case?
You see, perhaps you are asking that innocently, but I right off the bat see that being used to get people to kick you instead of taking the debuff. Get into a dungeon you don't like, say "hey, I'll only go up to that point, then I'll leave and you'll be screwed to find a replacement" and when they understandably say that's not acceptable you use that as reasoning to say they should kick you, since it's "them not wanting you in the group," to avoid taking the debuff and creating an excuse to not get a gameplay disruption ban.
If the rest of the group not being fine with your terms means you leave the group and take the debuff, though, all is fine.