Dates of Seceesion
While Lincoln arrived in February, early for his inauguration, it still wasn't to have taken place until March 3, 1861. And, certainly, the murder of the President-elect throws the Federal government (and the Nation) into an uproar
Also, Virginia didn't vote to for secession until April 17,1861.
If Lincoln is assassinated (with maybe his wife too?!) in Baltimore, in February 1861, I'll bet Virginia doesn't leave the Union.
This impacts other would-be Confederate states too.
In February 1861, the pro-secessionists in Tennessee's state government put it to a statewide vote - but it was rejected by a 54–46% margin. Only after Ft. Sumter was fired on, did Tennessee (informally on May 7 and formally in June 8, 1861) join the Confederacy.
And the State of Arkansas waited to May 6, 1861 to declare its secession.
Finally, North Carolina was (technically) the last state to secede on May 20, 1861.
Quite possibly, if there are still enough men of goodwill, this terrible event galvanizes the Nation and there is no Civil War.
Based of both Lincoln's public and private writings, I think we can say that he would have been willing to sacrifice his life in this manner if by that sacrifice he would have spared all the blood shed in the Civil War to come in OTL.