...provided you continue to update Linux and Xorg? https://nvidia.custhelp.com/app/answers/detail/a_id/3142/~/support-timeframes-for-unix-legacy-gpu-releases
The nvidia-340 is a closed-source binary-blob supported by Nvidia.
Nvidia can stop supporting it whenever they wish, so unless they open-source the source code, which is unlikely in my opinion, it'll stop receiving updates when they state & may not run on later linux kernels, or later software. It'll continue to operate on existing software, but updates in other software packages may cause issues if used with the non-updated Nvidia software.