If you have more then 1 entry at the final table the 2 will be added up to one big stack instead so you would have 1 seat at the final table.
When do “entry mergers” take place?
In non-Rush Poker Multi-Entry Tournaments, entry mergers will take place when your number of entries exceeds the number of tables left in the tournament. For example, if you have 15 entries on 15 different tables and one table breaks, two of your entries will be merged.
In Rush Poker Multi-Entry Tournaments, entry mergers will take place when the tournament field reaches a certain threshold. For example, in a nine-handed Rush Poker Multi-Entry Tournament that reaches the 90-player threshold, anyone with 11 entries will be merged to 10 entries. At the 81-player threshold, anyone with 10 entries will be merged to 9 entries, and so on.
The same goes for six-handed Rush Poker Multi-Entry Tournaments. At the 90-player threshold, anyone with 16 entries will be merged to 15 entries. At the 84-player threshold, anyone with 15 entries will be merged to 14 entries, and so on.
How are the finishing positions determined for “merged entries”?
When two of your entries are merged, the “merged entry” from the broken table is considered to be eliminated from the tournament. For example, if there are 18 entrants remaining after your entries have merged, your “merged entry” officially finishes the tournament in 19th place.
When a threshold is reached in a Rush Poker Multi-Entry Tournament, all “merged entries” at that threshold finish in the same position for the tournament. For example, when the 90-player threshold is reached, all “merged entries” finish tied for 91st place.
http://www.fulltiltpoker.com/multi-entry-tournaments you can read about it here!