The phrase "last legs" generally refers to something that is about to reach its end, or has reached a critical point. If you want to avoid repetition, there are several synonyms that can be used instead of "last legs." These include "on its last breath," "about to give out," "worn out," "on its final stretch," "at the end of its rope," "about to expire," "near its last gasp," "in its final throes," "about to collapse," "ready to croak," and "on its dying legs." These synonyms can be used to communicate a sense of urgency and impending conclusion or failure.