Gill as Test captain would be disastrous. But then, who are the options, really? Gill, Pant (irregular form, but regular in the team). Bumrah- best bet, regular form, but irregular in the team considering how much cricket we play. I'd vote for Bumrah as captain, but given the workload, he needs to let go of the T20 format.
That apart, there's literally no one who can fit in as captain, unless the selectors take a left field option and have someone as a stop gap solution. The others in the fray/not on the fray include:
Kohli- last legs, probably a home farewell in England looms
Rahul- the experiment has failed a few times, they will not go back to him
SKY- not even in the team
Shreyas- decent option, but needs to be in the team
Ruturaj- a good option, but not in the team yet.