Mercedes and GM had very strong pushrod engines that they developed. Good design, good materials, intake and exhausts that complimented each other, and these days, software to make it all work-an OHC design isn't really required to make power or to have durability.
Yes, at some point, probably H-D will have to go to water-cooling to meet tightening noise and pollution requirements. By then, the boomers (early 50's to age 71) and war babies (age now 71+) will be in their last round of buying bikes anyways. Will it matter to them that H-D goes "wet?" Only in that it's "more complexity and complications, and more to 'go wrong.'" And in my opinion, that's going to be a smaller group of buyers. The
Evo and later H-D buyers consist of boomers who are more-interested in reliability, and also the traditional appearance that has been so faithfully copied by the Japanese (Shadow, Vulcan, Intruder, Virago) to the Italians (Moto Guzzi California) and even the Germans (BMW-R1200C). The Gen X people and the Millennials will consider buying a Harley as a mark of "having made it," a status symbol of dispensable income for those who are interested in bikes. That was in my opinion one of the reasons so-many people bought the Harleys in the Evo era: new to motorcycling, and easy entry into a sub-group of the genre where the 'lifestyle' was as-important as the mode of transportation. Look at your local craigslist, and see how-many slightly-used H-D's there are, you'd have to be crazy to want to pay full list price for a new one, the choices for a cash buyer mean you can get a <10K miles nearly-new Twin Cam for 2/3 of what it cost new. And that's for something 5 years old, or less. Only the (relatively) rich will be buying a $40,000 CVO specialty Harley, new, I think. Any self-respecting potential Harley customer who is financially-observant will be scooping the cream off the top of the used low-mileage Harley's there are available now.
A new MI Harley dealership opens, 106,000 sq.ft.:
http://www.mlive.com/business/detroit/index.ssf/2016/08/see_inside_the_huge_new_harley.html#0
It's notable this store complex is on the site of a shuttered "largest retailer in the USA" Walton family business. They had to close it, but Harley thinks they can make their business plan for the parcel make money, where the Walton family struggled to. That doesn't sound like H-D is a company 'on the ropes' to me.