People who don't want to say "Inshallah" can instead simply say:

""Mā kullu mā yatamannā al-marʾu yudrikuhu, Tajrī al-riyāḥu bimā lā tashtahī al-sufunu." Not all that one wishes for is attained; the winds do not blow as the ships desire.

Okay, it's probably too long and there is nothing wrong with "Inshallah". I just like this beautiful little proverb with a related, but non religious meaning too (even though my Arabic is almost non existent). Try to practice saying it, even if you don't speak Arabic. Thanks to the nice rhyme and rhythm, it actually becomes really easy to remember after a while.

The author might be Al-Mutanabbi, but it was never confirmed and it could be a pre Islamic author.