Was the Civil War inevitable? What were options other than civil conflict? Why were they not viable?

I would argue that Civil War was inevitable, the reason being that it was the only viable way of resolving the issue of slavery once and for all.
A number of compromises had been tried in the past, but all they'd done was delay confronting the real issue at the heart of the problem. Even after the South seceded, attempts were made to cobble together yet another political compromise between the North and South on the issue of slavery. The so-called Corwin Amendment proposed to alter the Constitution so that all territory in the north would remain free of slavery while those territories in the south would receive federal protections for slavery.
Although this last-ditch measure garnered the support of President Lincoln, it was bitterly opposed by most of his fellow Republicans and failed to gain the required three-quarters support from all state legislatures for a constitutional amendment. This was largely because the Southern states had already seceded and so never got to vote on the proposal.
Had it passed, it would've entrenched the power of the slave states in the Union for generations to come. The fact that virtually no one in the South was interested in this latest attempt at compromise tells us that, at this point, the time for a political solution to the fraught issue of slavery was well and truly over.