IME most software will last that long, if it's remotely successful then it will at least make it to the 10 year mark. Business rarely changes drastically enough

IME most software will last that long, if it's remotely successful then it will at least make it to the 10 year mark. Business rarely changes drastically enough for a rewrite to make financial sense. About best you can hope for is a new "epoch" that forces a rewrite. In the MS world we went from classic VB and VC++ to .net, a lot of companies went through rewrites to keep up with that and some of that software is now nearing 20 years old. There has been a few other epoch like changes, terminal -> GUI, c++ -> java, desktop -> web, except for maybe the last one it's been quite a while since a new epoch has begun.