Head gaskets can fail in several ways. Many of the Subaru head gaskets leak externally and this is at least somewhat benign if the coolant level is kept up. This can usually be seen around the edges of the cylinder head and sometimes a wisp of steam or sweet smell may be present.
The other more serious type is a head gasket breach into the combustion chamber. This can cause overheating, serious loss of coolant, and all bets are off on how long a head gasket can hold up in this condition.
Just my opinion here, but I think the problems with Subaru head gaskets are due to a combination of things.
One is decreasing the number of head bolts and failure to retorque the head bolts after a certain mileage. At one time Subaru used to recommend and pay for a retorque on every new car at 1000 miles. The bean counters took care of that.
Subaru recommends (still does as far as I know) coating all replacement head gaskets with a sealer; something that is not done at the factory when new.
Subaru heads also seem to have a propensity to warp a bit out of specs. One would think that a short stubby cylinder head would not warp at all but my rough guess would be that of all the ones I've checked about 90% of them needed to be surfaced. A warped head will not seal properly of course; especially with no head bolt retorque being performed.
At one time Nissan did the same thing. They used to recommend and pay for a head bolt retorque. This procedure was eliminated and shortly afterwards the engines that did not get a retorque would start leaking oil from the pressure port that fed oil to the overhead camshaft.
If the coolant level is kept up and there are no serious overheating issues just drive it. If the leak is of the benign type you might consider adding a stop leak product to the cooling system. This could slow or even stop the leak.
Just my 2 cents and hope it helps.