All the Washington Post story basically does is report that some Lott allies have been mentioning the possibility of his leaving. As you point out, people have been doing so here. The article does nothing to suggest Lott himself is behind them.
If the ComPost had reason to believe he was, you may be sure they would mention it.
Have you noticed that the ComPost article specifically denies the report that was on CNN that Lott made the threat on the conference call? Shouldn't that tell you something?
The only thing I know about, for sure, is the Lott's words and actions. The rest is all window dressing and for supposition. This is being played out between Senate members, the WH and the Lott, behind the scenes.