It appears Toyota is going to review their program as their presence is based on Porsche being involved in LMP1.
http://classic.autosport.com/news/report.php/id/130956
I suspect there might be a few of the top LMP2 teams looking at a P1 program giving them a decent chance of an overall victory at Le Mans even if Toyota stay. I cannot see any new manufacturers before 2019 at the earliest but more likely they could wait for the new P1 regs.