Who is next Brahmadeva?
The present Sri Chaturmukha Brahmadeva has completed his 50 years in the Satyaloka (according to Brahmaloka calendar). He has another 50 years of lifespan. Everybody who has taken birth has to die. From Brahmadeva to Rudradeva all has to die. All of the Brahmanda (universe) has to be destroyed at some time. Just like we clean our house every now and then, Sri Hari who doesn't have death will clean our Brahmanda on each of the Mahakalpa. Except Sri Vishnu everything will perish.
After Sri Rama won the battle against Ravana reached Ayodhya with all his supporters including Sri Mukhyapranadeva (Sri Hanuman). After this Sri Rama gave aashirvaada to Sri Hanuman to become Sri Brahmadeva in the next Mahakalpa.
Similarly when Sri Bhimadeva (Bhima, the second of the Pandavas) killed the mighty Jarasandha. After this Sri Krishna gave the aashirvaada to Sri Bhimadeva to become next Sri Brahmadeva (Sri Bhimadeva is the avtaar of Vaayudeva, just like Sri Hanuman. Means Sri Bhimadeva and Sri Hanuman are the avataaras of Sri Mukhyapranadeva, that is Sri Vaayudeva).
Similarly the third avataar of Sri Mukhyapranadeva is Sri Madaanandateerthabhagavadpaadaachaarya (Sri Madhvacharya ji). When Sri Madhwacharya ji completed commentary on Brahmasutra Bhasya (originally written by Sri VedavyAsadevaru ) the avataara of Bhagavan Sri VedavyAsadevaru gave aashirvaada to Sri Madhvacharya ji to become next Sri Brahmadeva.
The different avataaras of Sri Vaayudeva is explained in Rigveda, Mahabharata, Vaayupurana and other granthas that Sri Hanuman, Sri Bhimadeva and Sri Madhvacharya ji are the one and the same and are the avataaras of Sri Vaayudeva.
Sri Gurubhyo namaha
Om Parabrahma Srimann Naaraayanaaya namaha