Oxidation of the beer is also likely to be minimal since it was just sitting still in the keg, rather than being sloshed around.
If you just lost the top of a triple-ripple or 3-part airlock but the liquid in the lock is still there, then you're fine.
If you lost the entire airlock, but the stopper or carboy cap is still on, unless the beer was lagering in an extremely dusty, dirty or moldy environment, you're probably also fine.
If the entire carboy or bucket was uncovered, then there's a chance you've lost the CO2 blanket and significant mold or bacteria got in. In that case, consider bottling if SG has dropped to about where you want it and if a sample doesn't taste green (i.e., notable diacetyl and/or acetaldehyde).
In any case, as the beer carbonates in the bottle, taste it periodically for signs of bacterial infection - thinner body, off-flavors, excessive carbonation. If you think that the batch is going bad, drink it soon!