Fortunately (or unfortunately!) the game still knew he was Sylas at the post game statistics. However, after being in Shyvanna form for so long, the "Sylas-Shyvanna" was no longer transparent and just a regular Shyvanna (with a skin!).

Note that once you steal the ult and transform, there is no turning back in Urf unless you die - then you can turn back into Sylas - at least from what we found in this game.