Is this an obvious 2nd molar(18) extraction? (photo)

I would never remove that tooth based on the information provided.  If there is no pain on biting it may be possible to avoid root canal as well with pulp cap and crown build-up.  The fracture will give the illusion of more severe decay.

This should be a routine root canal, crown build up filling and a crown on #18 without loss.  The tooth in front seems to also need a build up filling and crown but probably no root canal.  The decision to save the tooth or loose the tooth is YOURS and the dentists should give you advantages and disadvantages to options along with costs so YOU can make the right decision for YOU.Every dentist is an individual with individual experiences and abilities.  The good news is that you can always get another opinion to help your overall decision.

I would probably suggest an extraction. All of the decay would need to be removed before definitively determining if the tooth is salvageable or not, but you can usually expect decay to extend further than it appears on an xray.