In short, if a gap had opened up due to excessive wear you'd hear it.
Be aware that riding your bike without earplugs throws up all kinds of scary sounding stuff that you never notice with plugs in. I always think the bike is about to lunch itself when I do it.
I have a noisy tappet, had it since a few thousand miles, could be cam end float, could be a wide gap, it's got no worse in 16,000 miles. If something was wrong it'd get progressively worse over a relatively short period of time. In fact, I left an exhaust clearance deliberately wide on an older bike so I could have an early warning if they were closing up.