How many miles is an excellent question!!! "Rumor has it", based on my research of the subject, that 8,000 to 10,000 is about the expected life of a solid roller on the street. Interestingly, I lost a roller lifter at just over 8,000 miles myself, so the "data" appears to be accurate.
HOWEVER, I did NOT wipe out a cam lobe. The typical failure of a solid roller is the roller itself on the bottom of the lifter. Those tiny bearings fail due to lack of lubrication, the roller wheel stops turning, and the cam lobe "flat spots it" to the point of it breaking into several pieces. Leaving you with massive valve clearance on the valve that failed.
Wiping SEVERAL lobes of the cam itself does sound like something else is going on in this case. Of course my cam lobe was damaged, but "not that bad" actually, it was the failure of the lifter that was the real problem. While the new soild lifters have a provision for pressure feed oiling, which should enhance longevity of the tiny bearing and roller, I remain somewhat skeptical. Does that increase the life of the roller from 10,000 to 20,000 miles? 50,000 miles? How many more miles remains a bit of a mystery...
Personally, I like a flat tappet for a couple of reasons, the primary one being cost. It's cheap, compared to anything else. They are reliable ASSUMING you closely follow the breakin procedures AND stay on top of the
oil requirements (so they are a bit of a hassle all around). Hydro roller's seem to be fairly bullet proof and easy to setup, no hassle.
I like Comp Cam's myself. I suspect, like most ALL the cam grinders a few years back, Comp Cam's was still dealing with an industry wide problem(s) that have been largely addressed today. Lack of adequate ZDDP in the
oil being a primary problem, as well as to many folks running "cheap" lifters from overseas manufacturers that proved out later to be of inferior quality. THAT still holds true today, buy cheap lifters and your going to have trouble. DO NOT try to save any money on the lifters, go for the best you can get regardless of price.
Another problem with getting enough
oil to the lifter is how modern technology (engine building, windage trays and such) keeps the oil away from the crank. So your "splash" or "oil spray" from the crank to the camshaft lobe area is greatly reduced. Thereby starving the cam/lifters.