I've been thinking about it more and I intend to add a hard stop to the travel. I think the easiest thing will be to drill and tap the floating end of the leadscrew. I'll then turn a cup shape that fits the crest of the threads inside and covers 5mm of the screw thread (this will attach with a cap screw to the end of the leadscrew. Easily removable if needed and it will also prevent me from unthreading the cross slide from the end of the screw which is moderately annoying to get back on.
Thanks for the warning
I appreciate you guys looking out for me (or my machines more correctly).