So far I have played only against AI and have not encountered any stalemate situation, but I see the point of this thread.
What about adding one additional winning condition which only applies after the population pool is depleted? For instance one player could win if he/she controls a certain percentage of available construction sites (e.g. 85 %) after the population has run out? In that case no player can turtle in his main base since the other player can then easily capture all the other construction sites and so win the battle.
