Onions shouldn't degrade that quickly at room temperature anyhow, even if they weren't partially dried. This food safety and preservation site specifically addresses inadequately dried foods:
Check containers within seven to 10 days to see if moisture is
present. If you see moisture, remove food and redry at 140 to 160
degrees Fahrenheit. If food is moldy, discard it, throw away the
plastic freezer bag or sterilize the jar.
So, if your onions were partially dried, it should be safe to continue drying them. If they weren't very dry yet, I'd treat them as fresh onions at room temperature, which should also be stable enough not to go bad overnight.
(By the way, I assume part of the motivation for this question may have to do with a well-known myth which was circulating a few years back about cut onions "attracting" bacteria. This is certainly false, and here's a food scientist's explanation in more detail. Unless you sliced the onions with a highly contaminated knife, there should be no danger.)