You’re unlikely to have issues unless an entire architecture loses support from your distro, and if you’re running x86_64, that isn’t going to happen for a long, long time. I’ve never been in a position where I couldn’t compile a new workable kernel for an existing system out of Gentoo’s repositories. The only time I’ve ever needed to put an upgrade aside for a few months involved a machine’s video card losing driver support from nvidia—I needed a few spare hours to make sure there were no issues while over to nouveau before I could install a new kernel.
Note that you can run an up-to-date userland on an older kernel, too, provided you make sensible software choices. Changes to the kernel are not supposed to break userspace—that’s meant to keep older software running on newer kernels, but it also works the other way around quite a bit of the time.