Once Jewish, always Jewish?

I feel like I have to say this, even though I’ve said it like a 100 times before. I’m in the conversion process, I’m also in my 20s (roaring 20s), which means, if things are to go the way they’re supposed to, I’m looking for 50 to 60 more years on this earth. I think about the future a lot, I wonder where will I be? Sometimes my thinking goes too far to the point of realizing that a good number of people I love and care about will not be in my life then and it is terrifying. Another question comes to mind is also, what if I go through a faith crisis in my future? What if I ceased to believe in G-d at some point in my life? What happens to my Judaism? Do I cease being Jewish? Will all this turn out to be for nothing, or will I still be able to call myself Jewish regardless of the ups and downs of faith? I know the answer is yes to those who were born and raised Jewish, but I’m here asking as a convert.