There's no chance relegation for Kilmarnock would be positive in the slightest.
Their finances are terrible as it is. They'd be competing against similar clubs looking for a 'fresh start' in Hibernian, Dundee United and St. Mirren and so would most likely be stuck down there for the foreseeable future. Much better to stay up and have that fresh start as a top flight team. Their squad isn't terrible in the way Dundee United's is, so no real need to "clear the decks". A few signings are needed, sure, but it's not too drastic. The hit they would take financially would be.