I've been a Mac user since OS 9. Until I got this PoS Dell because I was afraid my Macbook was going to bite it after five years and I couldn't budget in a Mac. I fucked up the trackpad software on Windows, because isn't Windows about the freedom to fuck up your OS, and was happily using Linux Mint until I got the 10 update. I installed it hoping it would fix my trackpad, it didn't, but it did render my Linux partition unbootable. I fixed the trackpad on my own. Linux is still borked and I had important files on there. The best thing I can say about Windows 10 is it isn't Windows 8.
Have a look at "system rescue cd". Basically, it'll let you boot into your linux installation (using a rescue kernel). Once there, just install grub again - it'll detect that windows installation and allow you to choose your os at boot time. http://www.sysresccd.org/SystemRescueCd_Homepage Alternatively, "Boot repair disk" may be able to do it for you automatically. Just give it a try.
I've used this successfully to repair a boot partition after a Windows re-install borked it. Always good to have a boot repair disc around just-in-case, if you're using a Linux bootloader.