Google Maps says it takes about 5 months on foot from Borneo to Lascaux. So it could have been the same person who left at New Year's and was back home by Christmas.
I’m not aware of studies involving radiocarbon dating of paved roads, so I can’t say conclusively, but I believe the leading hypothesis is that they didn’t exist 50,000 years ago.
No, not in the general timeframe being discussed. Most is SEA was connected by land to continental Asia. Even North America and Asia were connected by Beringia. It’s possible you could have even walked to Australia from Asia, though I might be mistaken about that.