Nigerian gas may close the supply gap, but it will definitely not be a full-fledged replacement, since the EU bought gas from Russia at the best price on the market. Even if the volumes are the same, the price will obviously be higher, which will also be a cause for dissatisfaction
The volumes will most probably also not be the same. And I find this a bigger problem than the prices.
The international prices have skyrocketed anyway for no reason: the gas hasn't change, just the Russians have decided to ask more for it (and in their unrealistically "strong" fiat too).
Imho the more sources the better: let there be competition. We can see where allowing the (Russian) monopoly got us.