In my experience, Inkscape can be used as a professional replacement for Illustrator. It has never crashed on me. There may be some limitations, but nothing super inconvenient or something there isn't a workaround for.
GIMP, on the other hand, is a mixed bag. I believe Krita is a much better candidate to be used professionally than GIMP. GIMP has an objectively bad UI, has weird quirks for very simple tasks, and is prone to crashes. I use GIMP for simple image editing and Krita for more complex projects. GIMP 3.0 is their best chance to fix their reputation and I'm hopeful it will deliver.
If you don't have time to try them yourself, follow creators who use them and check their workflow. I recommend Davies Media Design on YouTube for great videos on Inkscape especially.
Edit: No program is completely immune to crashes, it's good practice to routinely save projects no matter how stable or unstable the program is.
That is true. IIRC, Krita is the only one of the 3 that has native CMYK support.