Change chain with cassette or do nothing?
If chain wear is beyond 1% then you are probably looking at a new drivetrain including chainrings. I would just remount the old chain and get the full wear out of everything else.
As far as changing chain only the industry standard is wear between 0.5-0.75% if you change within this range the theory is you will prolong the life of the drivetrain and perhaps never have to change anything except the chain.
The likelihood of snapping a chain is not very high for normal everyday use.