Well I wouldn’t say it’s a foregone conclusion- Islam historically had no success converting Theravada Buddhist areas in Southeast Asia and even vajrayana Buddhism amongst the mongols prevailed over Islam, so there’s nothing specifically about Buddhism that leads to weaker cultural and religious identities that will be easy to displace. On the other hand, perhaps more contact with a vibrant primarily Buddhist culture to the south will preserve these northern Buddhists from assimilation and prevent the islamisation of the area. Also Jains don’t really do well in positions of rulership, it’s not a very state friendly philosophy.
While I would say that it is not necessarily a foregone conclusion to the degree that nothing is foregone truly in history, it still stands to reason that Islam and its associated states, did generally wipe out Buddhism when they had the position of power. Much of this is related to the conception that the Buddhist spread throughout Asia was achieved through a very unique and different political climate to that period under Sassanid and later Caliphal authorities. Buddhism was itself dependent upon the diffusion through tolerant steppe, semi-steppe empires in Central Asia, such as the Kushans, the Arsacid, the Kangju-Sogdians, the Han Dynasty, the varied Saka regimes and the remnant Xiognu territories.
Without these vectors of transmission, the Buddhists of later times wee harried on the western edges by the Sassanid Empire and its anti-Buddhist policies and its expansionism, which harmed the ability of Buddhism to spread further west. Adding to this, was the changes within Hindustan, which saw Buddhism decline somewhat in its favor. The best opportunity for revival would be a scenario wherein the Hepthalites, taking the mantle of the Kushans, promote Buddhism to some degree and conquer much of the Sassanid empire and likewise counter the Gupta empire within Magadha, allowing a renewed Bactro-steppe-Saka hegemony over Hindustan and Central Asia, reopening the Silk Road and so forth.
If we wait until later times, our conditions would rely upon changing internal issues in Hindustan, a new Eranshahr, under a Buddhist or more tolerant dynasty or a no Islam scenario wherein Tibet is able to conquer Bactria, Tocharia and push influence into Hindustan. another option, is the route of 'Mahakhitan', using the Liao Dynasty to decimate Islam within the Indus region. Yet, this is using many variables on success of a single people. It is better to simply cut the head of the serpent, that being the Sassanid empire and the Caliphates.