I know no grounds for such an opinion--but several against it.

At Modder Cronje abandoned his lines, knowing that he had other and stronger ones behind him.

At Magersfontein a level plain lay behind the Boer position, and to abandon it was to give up the game altogether.
Besides, why should he abandon it?
He knew that he had hit us hard.

We had made absolutely no impression upon his defences.

Is it likely that he would have tamely given up all his advantages and surrendered the fruits of his victory without a struggle?
It is enough to mourn a defeat without the additional agony of thinking that a little more perseverance might have turned it into a victory.