Can the Government perform a T4C on the current contractor who has surrendered the award and go back to the pool of candidates and award to the next highest offeror?
Unfortunately it's not that simple. Once the period for submission of offers had closed, it must be assumed other potential offerors who did not respond to the original solicitation may be in a positon to submit an offer now. In that case, not re-opening the solicitation would be considered a restriction of competitive opportunity and could invite a protest. If the contracting officer can justify the urgency of the Government's requirement under the current circumstances, he/she can consider using the J&A procedures in FAR Part 6 (over the SAT) or FAR 13.106(b) (under the SAT).