The cassette is probably just worn by the worn chain but won't explode, thing to worry about would be chainring wear if you've left the chain far too long. I reckon that as the whole cassette moves as one it's probably play in the freehub.
@snottyotter started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
The cassette is probably just worn by the worn chain but won't explode, thing to worry about would be chainring wear if you've left the chain far too long. I reckon that as the whole cassette moves as one it's probably play in the freehub.