I (once) landed without a landing clearance. It's probably not legal and normally not safe. But the situation didn't look like a go around, so I decided that we touched down.
It was a perfect sunny day but with lots of traffic on an international airport. TWR was giving everyone clearances but he was continously talking, so we couldn't interrupt him for a hint to issue the landing clearance. There was no traffic on our runway and it looked like there wasn't any on our go around path. After vacating he ordered us to change to GND freq and it looked like he hadn't realized that he didn't give as the landing clearance. I didn't fill out a report.
So I would say I don't do a go around if it doesn't seem to be appropriate but remain cautious. If you are in doubt, do a go around.
Late landing clearances are pretty common in nowadays busy ATC environment. I estimate I have received a few dozens of landing clerances between 200 and 50 ft. I've never heard that there is a hard minimum for the landing clearance.
Dani