If he has the money, he should do that. He doesn't need voters' DOBs or SSNs to prove that they voted in both the Republican and Democratic primaries. But I suspect he doesn't have the money, or else he would not have pursued the mandamus filing.
2. Concede
He won't. And if he really has evidence of illegal votes, he shouldn't.
3. Take the mountain of evidence in possession now and file the legal challenge to the election. His attorney's said yesterday enough evidence exists to challenge the election and that they will challenge it.
If he has enough evidence to challenge the election, he should do that, and I'm sure he will. But I suspect he doesn't have quite enough evidence yet to overturn the election, because otherwise he would have filed the election challenge already and wouldn't have been pursuing the mandamus route. Time will tell.
4. Join the True The Vote lawsuit in federal court and obtain the nonredacted original poll books.
The argument for obtaining unredacted voter rolls is stronger under federal law than Mississippi law, so this is certainly an option for him. Downside is that federal court moves slowly, and he may not have enough time to wait for a federal decision.
5. Obtain a federal injunction allowing for an independent campaign or a write-in campaign.
Not a serious option, IMHO. "Sore loser" laws like Mississippi's have been upheld against constitutional challenges.
In reply to your comment on option 1, see #44.
In reply to your comment on option 4, federal courts do not allow their decisions to be rendered moot due to state procedural deadlines. Federal ‘Tolling’ provisions in effect put states in suspension until a federal order has been entered, and then the time clock starts clicking on the next court day following the order.
Further to option 4, federal courts hearing election cases understand the importance of time and will accommodate high profile cases to an expedited schedule.
In reply to your comment on option 5, there are many federal court rulings upholding serious substantial candidates for federal office. These cases hinge on noy allowing state laws to foreclose on a serious candidate’s options and on not disenfranchising a large number of voters who voted for a candidate for federal office. In this case there are hundreds and hundreds of thousands of voters who would be disenfranchised.