"It's not that the people of Hastings don't know what can be done - it was being done; it was proven. That's what's so disappointing to me, having put all the work into it, and getting it doing what it was planned for, and achieving very well," he said.
"We really had the right people producing top calibre results. To have it suspended in one day was a big disappointment, alright."
Sir Selwyn said he was due to meet with Hastings Mayor Lawrence Yule next week for a briefing on the options available to the council and until then was not in a position to offer a view on how the issue should be addressed.
Councillors will also meet next week to discuss the situation and consider a "community engagement process" ahead of a decision on juggling finances that are currently earmarked for other major projects: the development of Civic Square and building a CBD hotel.
Mr Yule said a contribution from central government funding to help with the Opera House strengthening work was a possibility "but it's really early stages yet - there are a number of buildings in New Zealand facing exactly this scenario".
Because the Opera House and Municipal Building were both category 1 historic buildings, they were in the highest category to receive government support "if there was ever some available".
Demolishing the buildings would be a "massive call" and a decision on what would ultimately happen on the site would probably not be made until late this year after a significant round of consultation with the public, he said.
"Nothing is on or off the table. We've got an issue we've got to deal with.
"We're really keen to understand what the community think about this ... understand what's available potentially from other funding sources - that's all part of the mix."