I bought a bunch of mostly cheapo bikes from a police auction a few months back. One had a rather hefty and fancy looking bike cable wrapped around the seatstays, key long gone. I was curious, so I took my plain hand held wire snips, the type used to snip off excess guitar string from the pegs, and decided to cut off the thick stainless cable.

It took less than a minute of moderate nibbling to cut the thing completely off. Using a tool that easily fits in my back pocket.