Well North Wales is having 4 regions going into lockdown so that will put the spanner in that! This is idiocy by the Welsh Government - destroying leisure transport, and hence, business! The question is how far back this puts us on the road to revory? 5 years? 10 years?
It depends on where you class as being back to recovered.
It probably also depends on what happens coming out the other side.
For instance if the airlines are hit hard (I know not an overly big thing for much of Wales) then it could well be that air travel is more expensive. If that's the case then travel within the UK may increase, however even if it doesn't chances are there'll be more travel within the UK by rail as there's less likely to be the air routes.
Either way that could actually increase rail passenger flows on some routes.
Likewise if more people holiday in the UK then that could also increase passenger flows.
WFH will harm rail travel, however most who do it wouldn't be doing so for more than 80% of the time and so the impact will be reduced from the maximum number of jobs which can be done from home. Especially given that not everyone will opt to take advantage of WFH when they can (my whole department would rather be in the office of they can be and I design roads which we've been able to do from home during the hard lockdown).
Others in other companies (who haven't gone back) would like to be back in, as they've identified that there's other relationships which they have which are useful to have but they don't have a reason to call (zoom, teams, etc.) those individuals.
Others have realised, due to being made redundant, that by living a simpler life they can live on a lower income and can still do simple but enjoyable things.
Others have realised that they were wasting a lot of money in travel costs and so like working from home, however they may also realise that working locally can get you the best of both worlds. This may result in needing to take a pay cut to do so, however given the time and cost saving from not working a long way from home they could find that they are better off than they were before.
Things are going to changes and some of them will negatively impact on rail travel, however other changes will positively impact on rail travel.
Overall, once there's almost no restrictions, chances are is likely to be 3 - 5 years before we're close to or at 2019 passenger miles traveled. That's likely to still be another free years to reach actual journey numbers, it's just that there's likely to be less shorter travel and more longer travel.
As an example there's likely to be less within M25 rail travel due to reduced commuting, however there could be more miles travel but less frequently from (say) Derbyshire to London to go into the office for 3 days every few weeks.
Chances are some routes (such as some within the SWR network) may take 10 - 15 years to recover to 2019 numbers and the peaks may even take longer than that to recover. However peak time trains with 50% now people than seats on then probably isn't a great idea.
Of course the other side of the coin is that if we're traveling less then rail may work out well for many due to the high upfront cost of car ownership (especially among those with limited no claims bonuses, were insurance can be over £1,000).
Driving 30 miles a day to get to and from work is about 7,000 miles a year. If you reduce that to 4,000 miles (3/5 days in the office) then the cost per mile of the car goes up significantly. That's fine if you use that car a lot on none work days, however if it isn't and it's now going to be say idle or very lightly used for 3 or 4 days a week some might consider is it needed. Especially if there's more than one car in the household.
It's unlikely that all those miles would be replaced by rail travel, however if everyone increased their rail miles by under 200 miles a year we'd increase by 15% the numbers of miles traveled by rail.
Some would do that easily, with a single trip to see friends or family. Others might go for more day trips by train a few times a year to achieve this. Others might not increase their use of trail at all and their miles are undertaken by others.
Now that 15% isn't likely to be increasing rail travel above the 2019 figures, but rather making so that (say) in 2022 rail use isn't as low as it otherwise would be.
As such, and especially given that we need to reduce our carbon emissions and public transport can a that very well, public transport will recover in time, however just don't expect it in 2023 to be the same as 2019.