Realisticly, with the diplomatic skills in this group, I think we have a chance of at least getting some force from Delve. Some things to consider:
1. They may not send a force with us, but even if they're not under out command, they're still helping us by hurting the gnolls. I agree that they may not put them under our command, but even if we don't have power over them they're still helping us.
2. We need to present them with a plan if we want help. Just saying "hey, there's some gnolls. You might want to stop them." Isn't going to help much. We need to give them a plan. Outline what the force would need to do, who would lead it, what they would get out of it, etc. and negotiate from there.
Given that Oceas and Tyrm already want to stay in Delve, and that a lot of us don't want to abandon the gnoll problem, I say we leave Oceas, Tyrm, and any others who want to here, while Li, Ayla, the survivors, and anybody else who wants to stop by Greerson. After roughly 2 months in Greerson, we head back. Round trip that gives us roughly 4 months, say 5 to be safe. That gives plenty of time for the group in Delve to rally support, and we could come back stronger, with a bigger force, then before.