While you do still want a rugged laptop, ultimately it is better to make sure you have a fantastic recovery plan for when shit happens.
One way is to go fully virtualised. Treat your host operating system as a basic shell, and instead install yoru real software on a VM. We use VMWare Workstation, Virtual box or others would work too.
Now fix your backup/recovery strategy. Backup your entire VM frequently - daily is ideal. A good way is to make use linux for the host, and keep the VM itself on an LVM volume - then you can read-consistent copies using LVM snaphots in the background with no impact on the guest - no pausing, no shutdown needed. You might also want to do a file-level back from within the VM of your very important files as a double safeguard.
Now you are sorted. Your machine will die, and when it does, you simply buy new one, re-install a host, then recover your VM onto the new one.
This also gives you an excuse to get a fairly grunty laptop - running VMs gives it a real good workout.
- Waiting until 5 years is up is not a good idea (and I assume they don't want to give it to you up front). Who knows what will happen. Ask for it one year at a time - or even better one month at a time - in advance.
- Get tax advice. You are in dangerous territory.
- Asking for 10% of the profits is interesting but theres an old saying in business that the 20% owner gets paid what the 80% owner wants them to. Its hard to stop the owner (say) takinga big salary and depleting the profits that way.
- Consider a "roulette clause". With this, either party can offer to buy the other one out. The trick is that if they refuse, then you can demand they buy you out. This avoids stalemate, which is very destructive in this situation.
- Good luck!