Don't quit the game. Are your friends on the same datacentre as you? If so, use the cross-party PF. Sure, open world content you're snookered, but a lot of the game is instanced duty, so this will help with that. Then, after the 90 days are up, you can transfer on over to their world, assuming it isn't congested.

I agree the warnings could be more prominent, but please don't feel like you have to quit over that. There are interim solutions available, and cross-world linkshells I believe are in the works, so that'll give you another avenue to communicate with them.