You can't intelligently discuss cable monopolies without following the money and reading the franchise agreement. As near as Google and I can figure out, you need to read:

http://www.seattle.gov/cable/comcast_franchise_06.pdf

Is this the most recent revision? Who knows. That would take more effort than I'm willing to expend.

First of all the agreement I linked to at seattle.gov claims to be in effect until 2016. So until 2016 (or so) you can whine all you want but its just posturing until them. I donno enough about Seattle politics to know if the proposed candidate would be in office in 3 years? Also I don't know enough seattle politics to tell if the mayor really has any input. Some localities are more autocratic than other more anarchistic localities. So the mayor may or may not have much impact at all other than pure PR.

Secondly follow the money. Read section 11.1. Basically for CATV in Seattle there is a 5% sales tax on top of any and all other fees gathered by comcast and paid to the city. You can call it a fee or bribe or compensation or whatever but its basically a sales tax. The feds limit this local tax and there's the usual boilerplate about increasing if legally allowed etc.

You can estimate based on subscriber numbers and bills or the other way around as total comcast revenue times percentage of comcast subscribers located in Seattle, well whatever either way its a substantial amount of money. So, follow the money. Where is the candidate proposing to raise rates, implement new taxes, or cut services if they kick out Comcast completely?