That looks like the bottom slice with intact roots. If so I'm not certain what might grow from it as typically a whole blub is used. Be interesting to see what grows from it if anything. The mold shouldn't be a deterrent to growth once it's in the ground but I suspect that it will rot in the ground anyways.

I don't think mold is an issue. Plenty of mold spores in the soil. But DRY roots? If all the roots are dry, it sounds dead.

Plant it and see what happens.

Agree with woodrose. Plant it, what have you got to lose?

Depends on what you are expecting from this, sure you can experiment if you want. Generally, onions do not do well in plastic bags, they rot. Was it refrigerated? You could always cut off the bad roots if you are saying there are new good roots.

all plants/roots need air.. as much as moisture... air circulation is imperative with every plant... lack of air on roots is a bog.. where little grows .. other than bog plants.. its also why so many plants fail or fail to thrive in non draining clay soils....

you would use a plastic bag.. to increase humidity... but the is no reason to seal the bag... i usually set the pot in the bottom.. and stand the bag up.. open... sooo.. i suggest.. with further attempts.. dont seal the bag shut.. and you will probably have less issues with rot and bad things happening...

that said.. as noted above.. go for it.. whats to lose??? .. keep us posted...

i would probably also harden it off.. dont just rip it from the bag... and move it out to a low humidity furnace dry house... do it over a few days or week ...

sooo.. damp media.. pot it.. put it back in an open back for a few weeks while the water roots turn into soil/media roots... this will stress them.. so make it easy for them ...

again.. keep us posted..

ken

in other words.. once you give the plant some air movement.. the mold will probably go away.. its a condition specific to being in a sealed bag for too long... imo ...

ken