Storrow serves the northern end of downtown, govt center, and the financial district. Those are the more critical portions. Cut and cover is probably the best idea-- temporary roads would go over the espanalde, yes, but in the long run it would be gone forever.
I think when people argue for the removal of storrow they advocate the section between the Allston Tolls and Arlington Street. With the pike right there there is NO REASON for this section to exist, and the only reason it has any traffic is that people don't want to pay the $2 in Allston. That's it, the end.
To get rid of this demand:
1) Remove the Allston tolls, realign the pike along the train tracks, and construct a full interchange on the old CSX yard to Soilders Field Road. Possibly allow inbound traffic to get on/off at Pleasant St, Buick St and Agganis Way.
2) Reconfigure the University Road Storrow exit to be the outbound on-ramp for the pike.
3) Close the Mass Ave/Newbury on ramp, demolish the entire Charlesgate complex. Repurpose Newbury St's dead ends as on/off ramps. Rebuild the bridge over the pike only for inbound egress and access to Comm Ave. Even better would be to lower the pike in this section, allowing for the Muddy to run above it in a aqueduct and reconstruct Charlesgate as it was originality intended, but this would be far more $$$.
4) Build on/off ramps somewhere in Bay Village.
Overall volume shouldn't change, so there should be no problem repurposing Storrows major points of egress for the pike. The traffic would still be the same, just coming off a different highway.