I'll tell you about my experience with this question. Before I got ill, I honestly never really thought about it; mostly because, as most young people do, I felt fairly invincible. When you have your health and youth, you don't really dwell on "what ifs" - you live in the moment and even with faith in God, you just don't consider much in the way of serious (I mean life-altering) trials.
So when I was slammed with a debilitating illness that had no name (at least until it was diagnosed!), there were so so many "what ifs" and a multitude of ways to question God. Will I get better? Am I dying? Will the pain stop? Will I be able to care for my children? Is there a cure for what is ailing me? And so many more....
The question of "What happens if I don't have enough faith to make it through..." never crossed my mind in the beginning of my disease. I KNEW God was with me, I knew that He orchestrated my life from beginning to end and this was a part of it. I didn't know WHY, but I knew who God was and His character and that He wouldn't abandon me even when I felt the most helpless and in the most pain. I grew a lot - God GAVE me the faith and molded it and shaped it and raised it up during those awful years of unexplained illness. He used friends and family to come around us and help with all the physical things I just wasn't able to do.
Then I was diagnosed and commenced with treatment. Treatment can be just as awful. New pains and ugly symptoms arise and while you KNOW you're getting better, it's hard some days to put the pills down the hatch. Lyme disease is such a WICKED disease. This is when the "What if I don't have the faith to....'s" started for me. I had tasted glimpses of feeling good only to be plunged back into yuckiness and I had 2 young kids now instead of one so each day my mind would play wars as I psyched myself up to roll out of bed. What if I just can't make it today? What if my girls grow up thinking their mom never did anything for them? What if my girls only remember their mom laying on a couch? What if my girls only remember their mom being grouchy? What if I NEVER GET BETTER? These questions were all due to my lack of faith that God was taking care of me and that He KNEW my girls would have a mom like this during these years of their life. When I paused and looked, I COULD see His grace in my life and theirs and that for sure they were being cared for in just they ways they needed. And I saw many times that God allowed them to NOT need me in ways other children their age usually needed their parents. He allowed me to spend those years "on the couch" without doing "damage" to my little ones.
I don't think there will ever be a time on earth when we stop wondering about how much faith we'll have when trials arise, but I know we can get better at it. In my own life, I find that I go through many periods of trusting God through harry times and then have a few moments of slipping, only to be reminded that God has ALWAYS been faithful and is so much bigger than any of my "what ifs".
So take heart and take courage, and have faith that in any and all situations that you might find yourself in today, when you ask, "What if I don't have enough faith for ______________?" - God is able to GIVE you the faith you are lacking. Rest easy in His embrace and cast your anxieties on Him.