1. I can't find my Kitten. What if he is lost?
2. I can't find my Kitten. What he was lost?
3. I can't find my Kitten. What if he got lost?
They are all asking the question about the cat being lost, but there tenses seem to differ. 1. "What if he is lost," assumes that the cat is still, present tense, lost, 2. "What if he was lost," states that the cat at some point was lost and is found, and finally 3. "What if he got lost," is telling that he is near and had gotten lost but is now safe.