Would the fall of a great warrior be enough to halt the flow of battle, even stopping all together?

Only insofar as noticably losing their leader might precipitate one side breaking and routing from the battle, but this wouldn't per se end the fighting. The death of nobles, leaders and even kings on Early Medieval battlefields was far from unheard-of: Æthelstan's victory at the 925 Battle of Brunanburh was marked by the high tally of Danish, Scottish and Irish leaders killed there. It's implied that most were killed in battle specifically with the Mercian elements of Æthelstan's army, although some may have been ridden down in flight by "West-Saxons [who] in their ranks rode down the long long day the hateful people, chopping down the battle-fleers from behind so sorely with sharply ground swords." Indeed, the poem The Battle of Brunanburh states that:

The Mercians did not deny any of those warriors their hard hand-playing,

those who had sought their land with Anlaf across the blending of oars upon the bosom of the sea, fated to fighting.

Five young kings lay slain on the battlefield, put to sleep by the sword; likewise seven more of the earls of Anlaf, and an uncountable army, their sailors and Scots.

There the lord of the Northmen was put to flight, driven by need to the stem of his ship, with but a little army

The ship pressed into the water, the king departed thereonto the fallow flood, sparing his spirit.

Another Old English poem which gives us a detailed account of battle is The Battle of Maldon. The poem gives a detailed account of the events following the death of the English leader, Ealdorman Byrhtnoth. As might be expected, for some, the sight of Byrhtnoth's wounding and then killing causes some to panic and flee within the English ranks:

Then they retreated from the battle spineless in the fray.

There the son of Odda was first to flight,

Godric from the fight, and abandoned the good man who many times often given him a horse;

he leapt on the steed which his lord owned, in those trappings which he had no right to take,

and his brothers were with him, both running away,

Godwine and Godwig, caring not for the fight,

but they turned from the war and sought the forest,

flying into the fastness and protecting their lives,

and more men as well, more than was proper,

if they had remembered all their favors that Byrhtnoth had done for them to their glory.

This effect was not universal, however. Byrhtnoth's death inspired some of the English to fight even harder:

Then there the proud thanes went forth

uncowardly men hastened eagerly;

they all wished one of two things—

to give up their lives or revenge their dear lord

...

Still at the van stood Eadweard the tall, ready and eager, speaking boastful words

that he would not flee a foot of land, or bend backwards while his superior lay dead.

He broke the Viking shield-wall and with their warriors fought.

until he had worthily avenged his treasure-giver upon the sea-men, before he too lay dead among the slain.

A similar situation occurs during the 1066 Battle of Hastings. Believing Duke William to have been killed in a charge against the English shield wall, the left wing of his army begins to waver and flee. William of Jumieges' Gesta Normanorum Ducum recorded:

At length the indomitable bravery of the English threw the Bretons, both horse and foot, and the other auxiliary troops composing the left wing, into confusion, and, in their rout, they drew with them almost all the rest of the duke's army, who, in their panic, believed that he was slain. The duke, perceiving that large bodies from the enemy had broken their ranks in pursuit of his flying troops, rode up to the fugitives and checked their retreat, loudly threatening them, and striking with his lance. Taking off his helmet, and exposing his naked head, he shouted : ' See, I am here ; I am still living, and, by God's help, shall yet have the victory.'

So: the death of a leader could certainly 'end' a battle insofar as it could affect the morale of the enemy and cause them to break and run, but it was unlikely in and of itself to actually cause a break in the fighting.