Regarding the following of Isa (AS) - Isa (AS) will subject himself to the leadership of the established Ummah - those who are in charge of the affairs of the majority at the time.
Even the majority can be slightly wrong or misaligned, but it does not mean that they will not be in charge, they will be guided by him to a correct position, but he (AS) will recognise their authenticity as inheritors of the faith. He will become the best of the ummah and hence we will follow his example as a follower in time.
It has to be made clear - A prophet guides, but the best follower shows how we should follow … first Isa (AS) was in the previous capacity and in his second coming he will return as a person in the second. Look to the examples of the great Caliphs - that will be the standard that we expect from Isa (AS) and some say better. He will be the best of the Ummatis.
The prophet Muhammad (SAW) instructed us to do things whereas his elect followers show us how we meet the instructions of RasoolAllah (SAW), by example. Personally I don’t feel the question or debate of sects will be important in those days … it will simply be a sheer struggle, the glimmer of hope coming from Isa (AS) amidst battle - people will have no time to speak about sectarian issues - they will simply do what is best and obvious based on the situation at hand.
Regarding the Arabic word for “return” yes I think I have not heard the term “ruju’” applied for his return - just “nuzul” - but it may be there. I was arguing about what was written earlier - that why can’t a new prophet return - I was talking about the fallacy in the statement.
Since his role will not be of a prophet but of a follower we acknowledge there is no more prophethood - the fact the he is named specifically to return we understand that to be true literally and that since Allah (SWT) is not unjust his title of prophet or his designation of (AS) will be unfitting to be taken away from him (AS).
If I ever have the benefit of meeting him (AS) I would address him as Ya Sayyidi Isa alaiKaSalam …