Define "make it". That it really is up to each one of us to define for ourselves. In my case, I'm in a band with 2 other guys that I've know for 25 years. We play very regularly, enough that it actually turns out to be a really good paying part time job. It more than covers my hobby expenses, and I have lot's of fun doing what I like, playing music. That was my goal. Yes, be realistic with your goals, but still set them and achieve them.
But about bands, and quitting them, and moving on...
I was in a 4 piece original band where the singer quit after we released 3 albums. The drummer was/is actually a very capable sing. So we did the Genesis move and carried on as a three piece and released 3 more albums. The moral of that story is sometimes members don't need to be replaced.
The drummer of the 3 piece original band decided he wanted to change musical directions and play rockabilly, something I enjoy, but wasn't wanting to commit to as a project. So I just took a break for a while and spent more time with the family. The moral of that story is that it's ok to take a break.
I was also in a cover band that went through 14 member changes over 3 years. We just never could get solid footing, and the constant tryouts and rehearsals to get new members up to speed just made it not fun anymore. The band finally folded and I moved on to the next project. The moral of that story is sometimes it's ok to end a project and start something new.
Like I said, I'm in a 3 piece cover band now that's been together for 4 years, and I've known the guys for 25 years. The drummer has actually been the drummer in every band I've been in. And when I haven't been in a band with him, we've still remained close friends. Aside from the cover gigs, we still write and record together, strictly for fun and to keep our writing chops up. In fact, while we had time to kill before a wedding gig, we recorded a music video for one of our original songs. It was fun and a great way to kill time. Anyway, as stated before, don't burn bridges. But more importantly, don't focus so much on the importance of the band, but focus on the people. If you've met someone who you've made a personal and musical connection with, keep them in your life. If there is at least one person you've enjoyed working with over the years, chances are you will probably get something going again with that person sooner than you think. It usually just happens that way. It's ok to end a band. The people will still be there, if you choose to keep in touch, etc.