So, while I can't predict the future, there is a strong chance that this offer will be on the table indefinitely.

Calculate this out over the term you plan to hold the property or just a "long time" if you have an indefinite plan.  

What type of strategy are you most interested in?Definitely

I'm told the tenant has no plans to vacate, and would like to continue to lease the space indefinitely.

Procurement and management services are included in the monthly fee and the owner has paid that fee for the full lease term.The owner has to pay the manager in this arrangement indefinitely, whether the manager performs services or not.  

You can always extend if needed but be careful allowing it indefinitely.

Having gone through several market cycles since being fully invested from 1988, both stock and real estate markets, I'd be cautious about expecting $8K per month in appreciation to continue indefinitely.

OTH  if his restaurant takes off he will be there in definitely and you will always be able to get a good rent.

Old town in definitely getting expensive, but occasionally there are places that hit the market that fall around your price range.

In addition, unless you have a deal lined up that will lock up your money indefinitely (Buy-and-Hold), a HELOC allows you to probably pay less in interest because it will only be partially utilized at any given time.