Even allowing for what has happened to the industry this year - I can't see MAG spending the money to extend T1, when the plan was for it to be mothballed pretty soon after the entirety of the T2 works were complete. The costs of demolishing that car park and rebuilding a new passenger handling structure in its place would be significant, and I can't see that it make financial sense when they've already accepted that T1 needs to go, and that it's likely that terminal capacity is going to be much less of an issue for the foreseeable.
Your concerns are valid. But if we acknowledge that T1 in particular has had very little spent on it in recent times in expectation that it would be demolished in the not too distant future, then doing nothing cannot remain a viable option for much longer. The envelope has been pushed pretty much to the limit. So if a new-build terminal is off the menu (almost a certainty given the implied costs of that) then a significant refresh / refurb of T1/T3 actually IS itself the cheap option. If that complex has to serve for another 20 years (for example) - a highly likely scenario - and since it has already been neglected for a decade now, some money will have to be spent on it. It can't soldier on for much longer without some well overdue TLC. I'd heard (and stand to be corrected on this) that the original T1 car park will need to come down anyway (structure life-expired?). So that space could be used to extend capability for processing formalities re arriving and departing pax. This also brings significant operational cost savings, as ideally T3 would cease to be serviced as a check-in / arrivals point in its own right. Just one set of facilities needed to service the whole complex as one integrated larger terminal. The extension need not be an expensive showpiece structure. 'Functional' and 'low budget' would tick all the boxes. Ryanair encourages thrift in such developments too. No-frills carriers love that whole 'bus station' vibe.
On the matter of how quickly terminal capacity will be needed, I'd suggest that the return of business will be very uneven across different market sectors. Short-haul no-frills carriers will go for a 'landgrab' strategy, securing valuable peak-time slots where they can and grandfathering them to stake their future. This puts pressure on less flexible legacy competitors as well. They can do this with some confidence too, as previous recessions have shown that people DO still take vacations after a downturn - but they often choose to
trade down to a lower budget option for a couple of years. Hence cheapie flights to Spain and Turkey come back much stronger than upmarket offerings to Florida and the Caribbean. Business travel trades down too to a far greater extent than people realise. MAN needs to plan around the likelihood that an increased proportion of its customers will be using no-frills metal in the years to come. And that means that T1/T3 - the likely home of no-frills at MAN - must be tailored to cope with that market shift. Higher footfall, shorter dwell-times airside. It doesn't need to be an architectural showpiece. Cheap and reliable is the requirement. Boxy and functional is fine.
On the topic of new stands for Ryanair and easyJet based growth, is it not simpler to concrete some off terminal apron and bus?
Unfortunately, as MANFOD alludes to, the only land which could reasonably be converted for additional aircraft parking is located on the west side of the airport - much too distant to be a viable option for quick service no-frills turnarounds serviced from T1/T3. And the only land available close to the existing T3 footprint is that same area which has all those utilities routed beneath it. The problem there was never the cost of extending the pier structure itself - it was the cost of rerouting those utilities. And that challenge applies equally whether one were to build a structure or just remote hard stands over that space. So the real choice is stark: pay to reroute the utilities and expand capacity, or accept the existing limitations for the long term. I can't visualise any suitable spare land of sufficient size for aircraft parking adjacent to the T1 footprint.