Time frame for secondary fermentation

I was wondering how long I can let the beer in secondary fermentation? I have lots of brew on hand and I am in no rush to bottle or keg this beer. It is currently in a dark, cool room.

If I do have a spare keg is it a problem to allow it to sit in the keg for a few months?

 

Put it on CO2 in the keg and you're good for a few months. High OG beer even longer. A lightly hopped pale ale may lose some hop character over time.

 

Is it okay just to leave in the carboy?

 

You can leave it in the carboy, the amount of time depends on head space. A large surface area in the head space will allow oxidation to begin in a shorter time period than when the beer fills the carboy into the neck.

Filling the head space of the carboy with CO2, and refilling periodically, will lengthen the storage time.