What happens during the resolution of a spell instructing players to exchange life totals and a replacement effect occurs?

When a spell instructs players to exchange life totals, if a replacement effect is applicable, the effect modifies how that exchange occurs. In this case, the resolution of the spell will still proceed, but the replacement effect can alter the outcome of the exchange.

For instance, if a player has a replacement effect that says "If you would gain life, instead you gain zero life," this effect would still apply during the exchange. Consequently, although the exchange of life totals is processed, the resulting life totals may differ from what would normally occur due to the influence of that replacement effect.

This means that triggered abilities may occur as a result of the life total change, and the game state progresses without completely negating the exchange. In contrast, canceling the exchange or preventing life alteration altogether would not hold true under normal circumstances of spell resolution. Therefore, the presence of a replacement effect offers a nuanced interaction rather than outright negating the process of life exchange.