Lightroom 6.0 cannot be started anymore

There have been other reports of LR 6 previously installed in Mac OS 10.15 starting to crash. You can search the forums more thoroughly, but I don't recall definitive solutions.  

One possibility: LR 6 is trying to open the face-recognition module on startup, which no longer works due to an expired third-party software library license.  At least a couple of people have fixed this by resetting LR's preferences, so it startup in Library Grid view rather than the People view:

https://www.lightroomqueen.com/how-do-i-reset-lightrooms-preferences/ 

You won't be able to reinstall LR 6 on Mac OS 10.15, since 10.15 removed support for 32-bit programs, and the LR installer is 32-bit.  Some people have tried to install an older version of Mac OS in another partition, boot into that, install LR 6, then boot back into 10.15, but I haven't seen authoritative reports that LR would then work when you boot back into 10.15.  

You could also run Mac OS 10.14 in a virtual machine, with LR 6 installed in it:

https://www.pcmag.com/how-to/how-to-run-32-bit-apps-in-macos-catalina

"Is there ANY way of getting lightroom back and running? Both my camera and my laptop don't make too much sense without it"

The annual Adobe Photography plan is only a fraction of the combined annual cost of your laptop and camera, so if your camera and laptop don't have much value without LR, it might make economic sense to bite the bullet and subscribe.