I have a few pat answers for this, some that have been mentioned in the comments. Among them:
- Django Reinhardt was badly burned in a fire and had just two working fingers, and he became a master of jazz guitar.
- Tony Iommi of Black Sabbath lost the tips of two fretting fingers just before he quit his day job to become a professional musician, and has become well-regarded guitarist after. Iommi has made fake fingertips out of plastic bottles and started down-tuning in order to make things easier for him, and that low tuning has become a foundation for many genres of music.
- Angus Young is a very small person with very small hands, and he still makes tremendous music.
- Of all the left-handed guitarists I can name, some like Mark Knopfler play right-handed, some like Elizabeth Cotton play left-handed on guitars tuned like they're right-handed, and some like Jimi Hendrix left-handed on guitars tuned for left-handed.
So, my general message is "Don't let any this hold you back".
I'd go back and say that, yes, there are ways to use your index finger, but they aren't going to be the ways most use theirs. Consider the first-position A chord. You fret the B, G and D strings on the second fret. I often fret this with my index finger, leaving my other fingers open to ornament the chord in other ways. This is certainly within your capabilities.
That's just the first thing that comes to mind. You didn't mention what kind of music you desire to play, and the next steps would be far different if you wanted to be an acoustic singer-songwriter, a thrash-djent-doom player, or a shred master. Todd Wilcox has many other ideas on how to make this work for you, but we all want you to know that there are many ways to make it work for you.