I don’t think there’s much connection between a plane’s ability to do a sideslip and how well it glides. A sideslip is just what naturally happens if you apply opposite aileron and rudder inputs. I think the issue is just that it’s a rather acrobatic maneuver to perform in a large passenger jet.

Since a sideslip increses air resistance by essentially flying sideways, if I didn't know that it has been done, I'd say it might even break apart a (long, thin) plane that wasn't designed for it. And it still might, but at much higher speeds than close to landing.

It's not unheard of for airliners to use a sideslip when landing in a crosswind, so I don't think structural strength is likely to be an issue at landing speeds.

https://code7700.com/pdfs/bca/bca_cross_with_care_2015-06.pd...

Yes an airliner is not designed for it and could easily get into a deadly spin when doing it. Especially engines out because you have two huge surfaces blocking airflow. A glider can do it pretty naturally because of its extremely low stall speed.

But I wouldn't call it impossible that's all.