The Liberty Belle does not service Tom Sawyers island. It just circles the island. You get to Tom Sawyers Island on the raft boats that load by BTMRR. They are usually running until dark.
The LibertyBelle was taken for it's annual rehab (boiler inspection, deck teaking, etc) back in September. It was to be out of service for about 2 weeks, but they decided to do a full refurbishment on it. It has been in service since 1994 and has never had a full rehab (just the mini rehabs). There is some work that needs to be done on the hull itself so it should be out of service until about May of 2006. It is currently behind Big Thunder Mountain at the wet dock (the train bridge swings open and the boat can pass through). They will be moving it to Dry dock (where they can fully remove it from the water) behind the Contemporary, via tugs across the Seven Seas Lagoon and Bay Lake, as soon as they can get the hull secured.
As others have stated to the original OP this does not affect TSI as that is a seperate attraction with it's own transportation.