Sky Digital (purchased in 1999) not Sky+ or HD?

My mum's old Sky satellite system (not Sky + or HD) has just stopped working, the engineer is coming out tomorrow and I was just wondering if anyone knew, if it is irreparable, whether the replacement would be a new Sky+ box. The system that has just gone wrong was purchased in 1999 and I presume that it may prove too expensive to repair as it is now an obsolete model.