What would happen if I ate nothing but protein?

meat ,eggs and fish are protein and fat.

and vegetable are carbs.

so it's a moot question because you would be eating more than protein.

if you lose weight would be dependent on how many calories you eat

but it's more than likely that you would lose weight.

Cutting out food groups is a bad idea and too much protein puts a real strain on your kidneys. You also need carbs to give you energy, especially if you are exercising a lot. The Dukan diet is based on the principle you are considering but includes low fat dairy and some oatmeal and that phase is only short term. Maybe have a look at that but don't give up carbs and fat completely.

You definitely would but you'd also tax your kidneys quite a bit as well as have virtually no energy during your workouts, trust me. Carbs are needed as your primary source of energy and going "keto" isn't something for long term.

Too much protein will kill you, literally. You need to get everything man, not just proteins and vegetables.