If you don't want to bother with the bootloader like the other comment mentioned you can also just use the boot menu from the motherboard instead. You gotta mash f11 (or whatever it is on your motherboard) on boot when you want to go into Windows, but if you only need it every once in a while it is good enough.
What's actually happening here is Windows is setting its bootloader first in your EFI when it gets updated. Linux isn't gone, you just have to press the "boot another drive" button and boot to it, or go into your EFI setup and switch the bootloader back to the Linux one.
Linuxes do the same thing when updating their bootloader.
Note for the Ackshually crowd: If you're still booting MBR (which comes with the partition eating risk on dual boots) you have a system that is older than Windows 8 - 11+ years old, so eating the MBR is something you'll have to deal with unconventionally, as all modern systems, OS, and hardware expect you to be using EFI.
I really hate that Windows does this. Which is why when I decide to switch a machine to Linux it's the only OS allowed to boot to bare metal. Windows can go in a VM and suck it.
Not sure why, but your comment made me think about the first machine I switched to Linux. It was a laptop who's fan eventually had a bad bearing and needed to be replaced. Luckily it was still under warranty, so I sent the laptop in to get the fan replaced, and received my laptop back with Windows installed on it... I was so livid.
