It doesn't matter which company provides the warranty. When one or both are bankrupt, nobody will be getting parts or repairs. Diamond will almost certainly go to the wall soon if they don't get this solved. Thielert engines are not the answer given their unreliability.
Slapping a 165 HP engine in place of a 135 HP one will have it's own set of problems and getting it tested and certified by October sounds a bit rosy to me.