While Rhegion is likely to not be that hard to convince to accept the rescue expedition, tough they would probably ask for some kind of payment for the trouble, as things are they are unlikely to be actually actively helping. The same factors making them care not one way or the other wheter the Kimaians end up in the Adriatic or death and enslaved making them, well, not care one way or the other.
Rhegion ambition for Pithekousai is interesting, tough, as while some Oscans have managed to make their way there the map show that the town itself is still in Greek hands. While Kimaians pride would undoutebly make things more complicated I wonder if they're might not be some kind of deal to be made here: Rhegion would actually actively help, at least in some measure, and in exchange Pithekousai would be directly granted to them, without having to be resetled or a more substantive expedition mounted to expulse the Oscans after they had the time to grow roots on the island.
EDIT: Or maybe the Oscans have only swam to the smaller, nearer, islands, with Pithekousai still in greek hands and therefore an even more enticing price for Rhegion.