Good concerns/questions... I'm sorry to hear of the pain associated with the #19 area.
I'm sure your Oral Surgeon has no presumptive plans to remove the graft. He is undoubtedly wanting to get a good visual look at the area, and "likely" that is all he will do. Yes, it is possible that there could be infection or your graft just not proceeding as planned, and it could (but this is unlikely) be in need of being redone or replaced with a different material which is more compatible with your surrounding tissue, but this, again is unlikely.
But with your pain problem, something is causing it, and your Oral Surgeon undoubtedly just wants to find out the "why" of it's causing you pain. He or She may just want to look and flush the area with saline, and give you additional tips to assist with the area healing up.
You asked is the graft fails. Unlikely does this happen. But, if that were the case, there are other graft materials. And, some "take" or work bio-compatibly with your tissue, than others might. So, the graft area "could" be changed. However, this is unlikely. No inherent risks should be expected should a graft be changed.
Lastly, you bring up excellent & normal concerns, which we all would understandably have. But the likihood of changing the graft material, is nearly zero.
I would go see the Oral Surgeon though. They can reassure that this procedure/graft you had done is looking good or not. Prescribe another more specific antibiotic and or other rinse or medicament you may need, and help to resolve your situation, which IS FIXABLE, more readily! I hope this helps you. ( -:
*Please feel free to ask any additional follow up concerns should you have such - OK?