How do REITs cover the principal debt

So I was looking at a few REITs that have a lease expiry of 30-40 years. Given they have to payout 90% of distributable income, how do they cover the principal of the issued debt at the completion of the lease where they might not have access to the land anymore? And even if they are able to renew it, it would cost quite a bit for them to do so. Does that simply adversely affect distributions upon renewal?

Finally, I suppose NAV would drop as the property value would fall as we come closer to land expiry? As such, the share price would drop to maintain a fare PB value and therefore, dividend yield would rise. I suppose the elevated dividends for REITS with leased land should compensate for the decline in NAV over a long period?

Thanks!