The 90 days is mainly for comics that start the account and then never update it afterward. If you have around 10 pages or more and update at least occasionally you should be okay. There are several long running comics on Keenspace that have ended (http://oneoverzero.keenspace.com/
) that won't be deleted due to inactivity.
If this 90 day inactivity problem bothers you, just make yourself a buffer of say 20 pages/strips before you sign up. As long as the admins can see that you're serious you shouldn't have any problems.