Question

Good evening! 
I have several questions about the definition of a borrower:
1. It is explained by the Ritva on Kiddushin 47b that any lender, by Torah law, can retract. (Although regarding assuming liability for unavoidable accidents, the taking is considered a taking, as Tosafot says there.) This requires clarification: if so, in what respect does the renter’s right of use take effect? After all, he can always retract. (For presumably the Ritva’s rule applies to rental as well, and not only to borrowing.)
2. A borrower is excluded in the case of real estate, and Maimonides’ wording is that there is no borrowing with real estate (and not merely that it is excluded from liability). This requires clarification: if so, how is it possible to rent out real estate? Presumably rights of use stem from taking possession of the item—through that, a right of use is created, along with liability, as is evident from the medieval authorities (Rishonim) on Bava Metzia 36b, who tie liability for unavoidable accidents to the fact that he took it, and therefore there is no exemption of “what difference does it make to me whether the Angel of Death struck here or there.” And just as any buyer cannot void the sale after the item was lost through unavoidable circumstances, meaning that the right of use stems from having taken the item and not merely from having received permission and the right to use it. If so, insofar as no taking effect applies, how is the right of use created? Must we say that there are two different rights of use—one that stems from taking, and the other from the very agreement itself?
3. How is a renter exempt from liability for unavoidable accidents just because he pays? If the very fact that “all the benefit is his” creates liability for unavoidable accidents, then a borrower cannot be exempt, since he has taken the benefit. The fact that he pays is an external act of giving—so how does that remove the status of taking?