It's difficult to say, my fuse took just 4 weeks before it blew again, but it's our second car and as such is lightly used. At that point i realised it wasn't just a random fuse blown.

Taking the blower motor out to inspect whether it's sticking is actually straight forward, and will take about 20 mins. At the end of the day, fuses (even thermal ones) blow for a reason and unless you identify and fix the root cause it's just a matter of time before you're back where you started.

If the blower motor is free-running then the other thing which may cause it to draw more current and blow a thermal fuse could be a blocked pollen filter - which reduces the amount of air which can be sucked in, hence the motor has to work harder. Many of the non-dealership garages (i.e. kwikfit, etc) don't replace pollen filters during an annual service in my experience.