If Leveon doesn't sign the tag by November 13th, then he can't sign it and can't show up this year. That means that he has to sign before Week 11. However, he only needs to play 6 games to be eligible for Free Agency next year and counted as accruing a season. Thus, he could play 11, 12, 13, 14, 15, and 16, and sit out 17 and the playoffs. Now, whether that would affect how teams view him and his potential earning power next offseason is another story.
I read here (
Agent Answers Leveon Bell Questions), that games on the roster exempt list don't count. So, Bell might want to sign in week 10 because the Steelers are expected to put him on the roster exempt list for 2 weeks. If he signs at the last second and it put on the exempt list, then he'll only have 5 games and can be franchised for the same amount next year.
The other negotiation happening is over the roster exemption. The team and player have to negotiate a per game income prior to Leveon signing the franchise tag and reporting. Usually the player has the team over a barrel, but with how Conner has been performing, if he stays healthy, they don't need Bell as much. Therefore, they can just stand pat saying that they won't pay Leveon for his 2 weeks of roster exemption. His only course is to not sign the franchise tag, but after Nov 13th, he can't sign anymore and would not accrue a year, and could presumably be right back under the tag again. I'm not sure the Steelers would do that, but at this point I have no idea.
My best guess is that Leveon shows up on Oct 31st or after 4pm on the 30th after the trade deadline. That leaves 9 games in the season, so after 2 games of roster exemption he would still accrue 7. He might complain about the 2 games of exemption, but he probably needs at least 2 weeks to get up to speed. I would be surprised if he had more than 75% of the workload prior to week 13, and perhaps even longer. This season has turned into a hot mess for him and it probably wasn't smart holding out, but he made the choice he thought was right. We'll see if it pays off. This all changes if Conner gets hurt, then I expect the timetable for Leveon to move up drastically because this team wants to contend.