The big question is of course, how long this goes on for. A vaccine available in mass quantities tomorrow would end the immediate crisis and we could concentrate on the economy, a second wave of a more severe virus strain with a higher mortality rate would plunge us into a depression that would still affect our grandchildren.
Generally people will downgrade a step or two, first class to business, business to economy, full service to low cost. Long haul holiday destination to regional, regional to domestic. The problem experienced in the UK after the financial crisis was that people's spending levels didn't instantly rebound once things improved. Money saving habits were ingrained and once it was realised that supermarket own brands did the same job as premium ones, you didn't actually need to upgrade your cell phone every year and a take away with supermarket wine was as nice as a meal in a poncy restaurant, at 1/4 of the price, it was hard to justify going back to the old ways. This was especially applicable if you were caught with your pants down financially having little in the bank and heavy monthly commitments.
After this pandemic and worldwide depression I predict a much smaller airline industry to emerge, similar to before deregulation. Airlines without a very healthy balance sheet before this started, or government backing will go under. What’s left will be nationalised or subject to heavy controls regarding routes, timetables and fares.
For most A380s it’s almost certainly long term storage for a couple of years and only back on a few limited routes where the numbers add up, if and when it does return. A small number of airlines might have the critical mass in terms of viable routes to operate them on. The B777-300 becomes the new A380
Probably the final nail for the B737 MAX as well. Why waste billions in patching up a fundamentally flawed design for which future demand has evaporated ? There may have been a case for a solution when the order book was in the thousands, but not any more. The current number of narrow bodies already flying will be able to cope with the reduced demand and the lower oil price will extend the life of the older less efficient versions. Far fewer reasons to spend on a new airframe when there isn't that much difference in the operating cost vs a 10 year old model.
The US government will likely take over Boeing due to its importance to the economy and as a defence supplier. The downturn could be used to develop an all new replacement aircraft.
I believe that the future is now all twins, with A320/B737s being used to the limits of their range and B777-200/B787s taking over from there. These types are already in existence in significant numbers and economical to operate, even though fuel price won’t be much of an issue for a while. High density seating in the narrow bodies with 10 and 9 across in the Boeings, possibly a couple of rows of business class will be the new norm. The A350 may be a better aircraft than the B787 but it won't be able to compete with second hand B777/B787s being sold at fire sale prices by bankrupt or downsizing airlines. The newer and larger Airbus variants such as the A321NEO could replace widebodies on many routes which would be unable to sustain a 300 seat aircraft.
Suites and lie flat seats won’t be filling up anytime soon. A holiday is likely to be an annual trip to a short/mid range destination on a low cost airline, rather than long haul on a premium carrier. Domestic tourism replaces international holidays for many people. Bali and Fiji become exotic destinations rather than run of the mill for Australian travellers.