Run-flat tires usually don't get punctured badly enough for them to be ruined.
In the event that you need a tow truck, it's not that bad. You just call BMW Assist up and give them your info and they send the tow truck right away. It is not like Triple A where you have to wait hours just for it to come. BMW Assist and these other concierge services that come with luxury cars are MUCH faster. Usually, the tow truck arrives within 15 minutes of the phone call.
And if it helps at all, I am in a similar boat. My car comes with a spare tire, but it is a very pathetic donut. In the event of a flat tire, I would call Infiniti Roadside Assistance and have them tow my car to the nearest service station as I just do not trust the donut spare...it is super small and pathetic and just cannot even do half the job the stock 18" wheels do.