If the prophet never emerged as a major figure what are the consequences.
Indeed, basically everything since the Middle-Ages would be butterflied big time on third continents at the same time right from the starts.
I assume no crusades, less human suffering.
Well, Crusades were hardly the only violent event of the era.
Islamic conquests weren't that pretty on their own (the wars against Berbers were quite bloody), maintain and use of slavery at a point not seen since centuries, dynastic warfare, feudal desintegration, carolingian conquests, etc.
To choose, frankly, Crusades were maybe the least bloody event of this short (and non-exhaustive) list.
In a non-historical context, human suffering is eventually tied too much to human condition to be get rid of because someone forgot to preach for a religious principle.
Would a non Islamic Arab World have kept old learning which in otl led to the European Renaisance.
Probably, but differently.
Arabo-Islamic world transmission of knowledge was made in two times.
1) Gathering and translating Greco-Roman corpus. They weren't the only ones to do this (Carolingian renaissance did a good job at preserving latin corpus for instance) but they did on a bigger scale and with a direct access to ancient hellenistic sources (by conquest or proximity with Byzantium)
2) Arabo-Islamic proper discoveries : It didn't happened overnight of course, but after the first centuries and the stabilisation of Arabo-Islamic world, several important advancies were made, as in optics, mettallurgy, etc.
The existance of a cultural and economical continuum from Spain to India greatly helped the gathering, mix and eventually new discoveries in scientific matters.
Without Islam, the 1) part is still there : Byzantium mostly, but as well in Western Europe(while more latin minded than greek, and therefore less focused on strictly scientific issues). So, eventually, it would have been done.
The second part is more trickly : the new discoveries depended heavily from the context they were made, and likely to have their OTL development butterflied.
Furthermore, some proper development made in western world independently (as compass) from others cultures would be likely changed as well, as their premisses were dependent of 2).
You may have a delay (hard to guesstimate. I would say no more than one century, but that's unbackable) of discoveries, the gathering and appropriation of ancient knowledge taking longer.
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On another consequences, we had
a thread about that some times ago, and if you allow me to quote myself, there is what I tought then.
The immediate consequences (up to the VIII century) would be :
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Persia : Muslim conquest of the Sassanid Empire was really helped by a constant infighting or even civil war. Granted, they could likely recover from it, but I don't think they'll be able to launch a war as they did under Khorso II (that admittedly was the first reason of the decline of Sassanid in first place)
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Arabia : Even without Islam and OTL conquest motivation, Arabs are a potential threat. Neighboring provinces are still under-protected and likely to be raided.
Of course, without politically united Arabia, it's likely their neighbors would split it under spheres of influences as OTL, but with a likely continued Sassanid and Aksumite decline, you'll have eventually a regional domination of indigenous Arabs.
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ERE : While its control on Egypt and Syria was loose, I don't think that the provinces would pose much trouble if emperors continue a tolerant (genuine or not) policy regarding religion. But in the likely case of emperor being more rigorist or more struggling in the N-E of their empire for imposing their religious views...
Finally, it won't change many things about Italy or Western European possessions : Italy was quite troubled even before Lombards and theses are likely to hold firmly their new lands, but not to take more on South (and with Benevento being most likely taken back)
The same for Spania.
Agruably, these gains were partially due to the long lasting Persian War, but the ERE is in the VII exhausted as well and can't really do a counter-attack.
But I think the Byzantines possessions in western Mediterranean would keep being autonomous from Constantinople as they were.
Except that, and possible Arab raids, it's likely that the Empire would face Balkanic and Slavic invasions better than OTL
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Visigoths : As OTL most likely, they would ascend in civil war up to the end of VII century. Eventually a pretender more powerful would emerge, and the kingdom would keep its traditional sphere : Hispania, Western North Africa. Speaking of which...
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North Africa : Mostly Byzantine held, with Berber Kingdoms that slowly Christianize Visigoths and Byzantines. A great asset for Byzantines in their control of Mediterranean Basin.
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Francia : Without Islamic invasion of Spain, it's likely Aquitaine would survive (its existence being based on balance with Visigothic Spain, Wasconia and Francia). It wouldn't prevent the Frankish conquest of Frisia, Saxony or even Avars, that were largely independent of the Islamic threat southwards.
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Christianism : without Islam, without the fall of Visigothic Spain, and with Byzance strong enough to keep the Lombards in Northern Italy : it's likely the popes wouldn't have to call Franks to help against these latters.
While keeping an important influential role in the western Christianity (that was quite different from Greek rites already), the church would certainly be more "national" as OTL (aka, ruled by local clergy under royal guidance).
Something like autocephalous patriarchates, without partiarchs
