The plan was never to retain or refurbish T1 in any form- the entire purpose of the transformation programme is to replace T1 which is outdated, this is stated in the original planning application submitted in 2015.
The whole of T2 once finished will have a higher passenger capacity than the original T2 + T1 combined being capable of handling up to 35 million pax per annum alone.
T3 remains open for Ryanair, topping up MAN’s capacity over and above T2.
The stands on B pier will be split between some being walked from T3 and the rest being remote, C pier will also become remote stands.
Other than that there is no use for the site of T1 presently so it doesn’t make sense to spend a significant amount on demolition for a site that’s not going to be used anyway - similar to LHR T1 which is also mothballed.