On a very small sample size, I once estimated average 2nd chance participation at roughly 20% per game. This was back in December or earlier this year, when I was more gung-ho about 2nd chance drawings. My interest has waned quite a bit since then, mainly thanks to my 0-for-72 average.
Based on prizes and prizes claimed figures, DM is at 46.27% sold. Total ticket population is 21,600,000, thus ~9.99 million DM tickets sold. So, my guesstimate is ~2 million 2nd chance entries for DM. This game didn't sell anywhere close to its recent predecessors.
Our most recent real-life example was $1MF. 2nd chance entries for that game was actually less than 20%. Game was at 93.80% sold, total ticket population was 30,000,000, thus ~28,140,000 tickets sold. 2nd chance entry count was 4,847,997. 2nd chance participation rate for $1MF was 17.2%.
The $10 game before that, $250 Million Cash Spectacular, had 7,491,501 2nd chance entries. I don't have access to the game stats anymore, but I believe by the time that game ended it had 37 top prizes, and they were all claimed, so probably the game was close to 99% sold. Making that assumption, 2nd chance participation was 17.0% for this game.