In the Top Hatted Bloody Goon’s second inaugural mumbling he admitted he refused to negotiate with Southern agents in 1861. It didn’t fit his war lust agenda.
There is no republican candidate who would have done much different than Lincoln. Do you really think Chase or Seward would have just let the south walk away? No one in the Republican Party at that time believed that secession due to a party you didn’t like winning the presidency was legal.
You don’t negotiate with an illegal government that no nation on earth recognizes as legitimate.