Congress doesn't have many good politicians, Rahul Gandhi is clueless what he is doing, many politicians stole as much they can steal. At the wrong time, Modi came out of nowhere and making their life horrible. Their visibility in opposition is minimum. Other than a few media houses(Congress is needed in the panel), no one even needs them.
Congress still has unconditional support from prominent media houses, still has a legacy of good reform(but slow reform) and not being openly communal and a good PR about pro minority. I don't really think unless they do something radical(kick Gandhi family out of congress party), they won't be coming to power again.