Wheel clamp and steering wheel clamp to immobise the vehicle so it cant be just driven away.
Order a new key from your local dealership, remember to take in all your documents.
When the new key arrives, book the vehicle in to have the tracks deleted on the keys and new tracks put on (if keys are chipped)
Have the work done, and after a couple of weeks MB database should be up to date with the latest key details so you can place the order for the 2nd new key.
If non-chipped key, get it booked in for a lock set change.
Slap the whole lot into your insurance company that SHOULD reimburse you with all costs.