If nuclear fusion makes electricity abundant in the future, is there still a need to worry about data center costs now?

Yes, there still is, because power supply and heat dissipation are two separate issues that need independent evaluation. The article considers nuclear fusion as a possible future direction to improve energy supply, but it doesn't provide a definite timeline for planning investments. Even if electricity becomes abundant, the heat generated by running servers still needs to be removed; according to the author's analysis, a hot climate requires cooling systems to work harder and cost more. Therefore, you can't treat an energy breakthrough that hasn't been confirmed as a basis for assuming all operational constraints will disappear.