sorry for a confusing title but i want to know - currently my roselia (planning to get a roserade as soon as possible) is receiving good training in iron cave double battles with riley battling with me. but is it possible to get him to follow me again after the event in iron island?

Nope. It's only temporary unless you do tag team in the battle tower with him but I don't recommend it.

quote Aquarys

unless you do tag team in the battle tower with him but I don't recommend it.

And the tag team in the battle tower doesn't give out any exp points, so it's not helpful for training anyway.

I think Riley will remain on iron island until you go all the way threw the cave, where he then gives you an egg and leaves. So if you wish to continue training just don't go to the end of the cave.

that sucks. it was so good training doing double battles with wild pokemon.... and i need to get further sometime... oh well thanks for the help guys

Actually, later on in the game you team up with a few other trainers as well.