Dan,
I have Hagerty Insurance for the Pagoda, agreed-value. They specifically plan for a collector to "buy back" the total loss, and provide for this eventuality. If you have a Pagoda valued at $70,000 (agreed value), and it is a "total loss" (which is some formula based on the cost to repair), they give you $70K less deductible and take the car away. You can buy it back for the salvage value; so if the wreck is deemed (my guess is from their adjusters) to be worth $7,500, then they'll add this to the deductible, subtract both from the agreed value, and write you the check.
BTW, for many years we did not own any other car other than the Mercedes; our daily drivers were management lease vehicles only. A letter from the HR department along with paperwork indicating the cars assigned sufficed to convince Hagerty that it is OK to write collector car insurance for me even when we don't own other cars or have other auto insurance. There are exceptions to the rule that Alfred pointed out. I will say that Hagerty was the only collector car specialty firm that would make this happen; the others couldn't wrap their heads around the concept. Being a Michigan-based company they were familiar with management lease vehicles and a collector car in the garage.