Most likely if a pilot didn't bid for a schedule for any particular month, he'd be assigned one (the leftover garbage most likely) rather than just getting nothing. They hired you to fly and intend for you to do just that.
If a person wanted an extended time off (other than military LOA which is another animal), there's usually a contractual definition of how long it can be and under what circumstances...to be arranged per the contract process.
IIRC, our contract allowed 180 days unpaid leave. If you went longer than that, you started losing seniority numbers (sliding backward) for every month (or even part of a month maybe...can't remember).
This stuff varies with each airline and contract.