No brainer: if he has to chose 1/2, RG is the only reasonable option. Eu has opened its internal borders while people from America are not allowed in without quarantine. Needless to say he has better chance to successfully defend RG.
If current situation in US wrt the virus stats does not change in next few weeks (very likely) we can expect very few international players to participate in USO this year. Who would voluntarily subject themselves to 2 week quarantine? So, USO will likely be US (and maybe Canadian) players contest. Finally we may have an American major winner, whom we've been waiting for so long (since Agassi in 2004). And vice versa: no or hardly any, Americans at RG. If the situation does not change much for rest of the year, we may see largely Australian-only AO! An unforeseen opportunity for Nick/Deminor! Both can freely travel to Melbourne and back home as NSW/ACT/VIC borders are open. Finally the Big3 reign will be broken: strangely not by the second gen displacing them on the court but by the a virus. The current No1 was already potentially displaced, IMO. Joker, even if he physically recovers 100%, I suspect the mental pressure of everybody criticising and booing him and a collapse of his PR image, is likely to take a toll and prevent from performing at top level.