If player A place a Town Track Tile on a Town Hex with two exits straight(type #T21 on rules) the track that exits from town becomes incomplete(another player can't connect). Later if not extended it becomes unowned and another player can't connect because the rules says you can only claim an unowned,incomplete link if either starts at a city or directly connects to one of your own links.
So the question is: The other players can connect to this town only through a new track(replacing the town tile with an improvement).Is it right?
I am fairly sure that you have to build into a town to place a town tile so one of the "exits" will be owned by the person placing the tile.
If they don't continue building the other exit/exits will become unowned.
Another player can build to it from somewhere else (i.e. connecting to the town tile via the unowned link by directly connecting to the unowned link). However they could also build to the town by an alternate route (replacing the town tile with an alternate one with more exits that respects the existing exits). In this case they could then build out of the unowned exit (as could the original player who is still connected to the town)