Narendra Modi is undoubtedly now the Political Leadership face in India. There is no other leader outside and inside BJP who can equal his charisma. But with the BJP's own rules of not having a leader continue at helm after a certain age limit, the chances of Narendra Modi returning as PM if BJP gets majority is slimmer. Having said that, with current global turmoil on so many fronts (COVID-19, Afghan war, Climate crisis) it may be wise to continue with a leader who has proven his mettle and understands the ground reality better than anyone else.
It may be tough for a new leader even within BJP as he/she needs to get up to speed (and time is of prime essence at this point). Every minute counts and we may miss the train in terms of taking critical decisions for the country and in global stage plus making important foreign policy changes may take longer from a new leader.
What about the economic reforms currently underway under Modi?
Yes, this is another important question. Although the new leader if from BJP itself will have similar plans to review economy, there may be slight change in approach. So as far as the economic reforms are concerned it should not be a pain topic if BJP itself comes to power again.
Does BJP's outlook as a party change if Modi is not at the helm?
To a certain extent yes. People have Modi imprinted in their brains, to get used to a new face and more importantly to have the conviction that "this new guy from BJP is a true warrior like Modi" will take time. Problem is India doesn't have time in global stage, we have to keep running at the same or even better pace year-over-year. If the growth engine slows down even at a very small percentage, we will lag behind other players like China.
Conclusion: Yes Modi is needed for now and it’s all going good. The reality is he has to retire very soon and on that day we may experience some slowness in the administration until the new leader picks up the pace to runs (hopefully) even faster than Modi for the country.