I should say they'd better inform about the closures through DB app. I had no clues the line was closed before the 27th of April when I went here on the 17th.

Echt scheiße.

I can only recommend for the future that you look at the local carrier's site and/or social media before departure and not rely on a general site like DB.
But don't worry: RNV's network is hugely varied and you will find lots of different types of trams, which you hardly see elsewhere.
Bad Dürkheim happens to be a region where I visit occasionally on holiday. With every season, weather and sun position, you can discover new photo positions. Not to mention line 5...
In September there is a sausage market, which is a disguise for a huge wine festival. I'll stay away from there then (because of far too busy) but then keep an eye on the timetable: in previous years, the frequency to Bad Dürkheim was increased during that period (and certainly at weekends), sometimes to a 10 - 15-minute service. And be sure: there will be no track works then.