There is a long thread about this topic.

My opinion.
Any such arrangements as sell back should be agreed with the dealer in advance. As part of the buying. Probably he wan't buy it back, but can sell it for you for a provision. He should also the help with transfer of ownership and other formalism. The dealer should fix this for you. To do this yourself buying from a private persons require quite some knowledge of all procedures and good Spanish. But of course possible. To sell private will also require some knowledge and maybe a lot of time.

You can't leave Chile until you have the formal documents as owner. I have heard that it may take 4 weeks for new bikes and 8 weeks for used bikes. But if you buy from a dealer(that I recommend you do. Ask him). Or if someone in forum has done this lately has updated information. The temporary documents can only be used inside Chile.
Take a tour along Caretera Austral to start with ?
While you wait for documents.

You can't sell it outside the country where you bought it. Then it would need to be exported and imported. Work + money. Not worth it.

You can never exit the country on a rented bike.

You do not mention how long time you will spend. Buying and selling takes time. Renting is for shorter period.

Where are you from ? There is good shipping service from Germany to Chile, if you are from Europe. To bring your own bike.
=
I know that the often there are posts proposal creative ideas of how to get around legal aspects. But......