After a trial account has been upgraded to a regular one you have to pay a sub fee every thirty days, so yes after the 30 days that comes with the purchase of ARR you will have to subscribe to keep playing. That said trial accounts have a number of restrictions on them beyond just the level 35 cap such as the gil cap, market board lock out, and inability to use /shout, /tell, /yell, in game mail or retainers.