It is not permissible for one who fears that he himself may die, or that someone whose life is protected according to Islamic law whom he could save may die, to continue praying, and he is sinning by doing that. If he dies or is injured, then he is regarded as having thrown himself into destruction.

Thinking to oneself whilst praying about things that have nothing to do with the prayer detracts from its reward, but it does not invalidate the prayer altogether.