Voiding the whole season (and other tiers) is the only completely fair thing to do, which is unfortunate as I do think Liverpool should get the title. However, if there is no possibility to resume and finish the season by July or so, with the transfer windows altered for a season, then the full void simply has to happen.
This opens up the least can of worms as next season can begin as normal, the transfer windows can remain the same and players contracts ending in June can remain as is.
In regards to European places, you have to use the previous seasons.
The only issues are:
1) TV Packages - I'd like to think this is easy to resolve. Customers refunded for the remaining months and don't have access to the channels until June. Money given to the TV companies to compensate losses.
2) Record Keeping - This one is a bit less of an issue and would probably just stand. However, if the season is void, do we scrap the history of win/loss/draw records between teams and the goals/assists for every player?
I'd be more inclined to just give the players and teams the latter, but it's at least a question to ask albeit a rather moot point in the circumstances.
Any playoffs, average points, current standings, behind closed doors and whatever else just aren't feasible no matter what argument anyone comes up with IMO. You are always going to be more fair to one team than another which ruins the integrity of the competition. It either all happens as normal or none of it does. Those are the only two options, it's a waste of time debating anything else. Hopefully, this break grants enough time to find a way to resume, but I think the spread of the virus will worsen in that time frame so I expect a full season void.