The Shuriken itself is a standalone product. I'm unsure about reliability on the road, but mine is often connected to a Helix via the cable (no battery), and hasn't given me an issue. The Workbench HD software has worked alright on mine, but took a few extra minutes to install (I forget the reasons, but it wasn't as simple). It does, however, work just fine for me on both Win10 and 11, also thru the Helix, so I don't mind. If you find one that functions normally, just get it and enjoy; even if the electronics fail (eventually), the guitar itself is quite good, plus the routed areas could be filled with other technological things.
Regarding spare parts - I wonder if Line6 would sell to individual owners so they could perform their own work. One example is buying a replacement truss rod once for one of my guitars - not exactly a standard request, but even guitar manufacturers have been willing to send one to a "joe schmo" like me. I'd love to have a backup set of modules in the event one of mine fails and I'm unable to repair it.
I expect battery packs to be the biggest issue unless new ones with decent cells are available. I get about 6-8 hours of use from the battery that came with my shuriken, so I stopped using it after about a month and bought a longer VDI cable so I could keep playing. The life is supposed to be ~12 hours, and a 2-3 year shelf life. I suspect that mine sat in stock for a while and the battery may have been low charge. Who knows. But it's something to consider down the road, unless one just uses the VDI cable, at which point batteries are a nonissue. Plug it in like a regular guitar.
Buy one and see how you like it - even old Variax models are still kicking around reliably after ~20 years. That's saying something.