Since we're talking a bathroom the first thing I'd check for is a GFCI. When GFCI's first came out, the code allowed you to put just one in for the entire house. You'll typically find that all the bathroom receptacles, your outside and perhaps garage and basement receptacles all connected to a single one. That one may be in any of those locations. I'd look for one and press the reset on it to see if the problem goes away.

Wiring rarely breaks other than where there are connections made. Typically, you trace from the breaker out to each place where the wire would have a connection (usually receptacles, light boxes, or switches) to find the errant one.

One of my houses was wired with one GFCI breaker for 3 bathrooms and two outside outlets. Very confusing at first when a rainstorm tripped the circuit through the outside box and bath outlets did not work. I swapped to GFCI outlets that were wired to only protect each individual outlet.

Even if its not GFCI related, I would go back through and look at all the junction boxes on the circuit. Just turn off the circuit and work through finding what outlet or light no longer has electricity. The wiring itself will not break unless its under strain, so wiring in the walls hardly ever goes bad unless there is some renovation that disrupts it.

Bruce