It actually feels like there's more closures than there actually are. A lot of them are closed and relocated because their respective parks have closed for example.
Desert Race - Operational no issues
Formula Rossa - Remains closed, rumoured that its launch system is damaged. Has been down since February and the park have been very coy about what's actually going on
Furius Baco - Operational, no issues (beyond being an atrocious rollercoaster)
Kanonen - Relocated to the USA as Matugani
Kingda Ka - Rust in Pieces
Rita - Operational, no issues
Senzafito - Closed down due to the park closing completely. Now in Canada and converted to LSM launch.
Skycar - Operational no issues
Speed Monster - Operational, no issues
Stealth - Operational, no issues
Storm Runner - Operational, no issues
Superman The Escape - Operational, no issues
Top Thrill Dragster - I mean.. I'm not delivering lectures on this.
Xcelerator - It's currently operational. It spent over a year closed and under refurbishment and opened at the end of last year.
Zaturn - Park it was located at in Japan closed down, and the ride now sits in pieces in Russia.
I wouldn't worry about Stealth or Rita to be honest. As some of the later models, the technology is slightly perfected from the originals and I would say the reliability of both rides is far better than their American counterparts.