Retention Query

I have been with TCS for 12 years, having joined as a fresher. With only 15 days left before my separation, my manager has offered to retain me with a 60% salary increase and an onsite opportunity. However, I received a C band in my last evaluation due to RTO compliance and never received an A band despite working on that account for 5 years without any onsite opportunities. All communications regarding these matters have been verbal, with no written documentation. What should I do now? Please advise.