If you let your account lapse, you won't lose your Lotro house. Unfortunately, there are neighborhoods full of people who currently do not play, with locked out houses. On the one hand its nice for military personnel or just about every "average" player who jumps from game to game to game. You can rest a bit knowing your precious house won't be taken over by someone else. But you'll have to pay a pretty fee to unlock it when you return.
If you set your permissions to let others pay for you it will continue to not be locked out if you are not playing and someone else pays for you.
Best practice: pay up the 6 weeks before you go inactive, ask someone to keep an eye on it for you also. The lockout fee is only 1 extra week upkeep on top of accrued weekly upkeeps.