If TOR is able to maintain enough subs to survive 1 year, I expect the game to be pretty complete by then with enough compelling features besides voiced quests to attract and keep and grow its current player base. Until then, I see TOR as an ongoing experience : failure can be just around the corner but nothing is sure yet. After GW2 then MoP hit the market, things will be much tougher for Bioware. And any Titan-related announcement down the road can well put an abrupt end to TOR current success.
TOR need to really quickly build upon its already solid foundation or it will be destroyed by its most serious competitors in the monthes to come.