I''ve seen it done, but I didn''t think it was a very good idea then, and still don''t think so. Depending on how the mast is stayed, and, if the stays are adjusted correctly, and, if the stays are in good condition, the mast and
rig are probably strong enough, but a lot of things could go wrong that you might not anticipate. The halyard could be frayed and snap, or it might be cut by a sharp edge at the masthead, or a sheave might be damaged. If the
rig isn’t adjusted correctly, you could break the mast.
If you have a trailer, I agree with Jim that you should just pull the boat out and inspect it. If you don''t have a trailer and will have to pay to have the boat lifted out for inspection, perhaps you can delay it for a little while by leaving the keel all the way down, and sailing with it that way.
If the cable on a swing keel boat fails while the keel is in the up position, there is a real possibility that it will do serious damage to the boat, and/or cause it to sink. Lightly built fiberglass boats can’t take the stress of the sudden drop of a few hundred pounds of keel. If the condition of the keel mechanism is suspect, you would probably be better off to just bite the bullet, have it lifted out, and inspect and repair it.