nit pick, but this isnt true at all. "Base load generation" refers to fixed capacity generators (coal, nukes) that run at 100%, matched to the lowest point of the demand curve overnight. This is an obsolete concept in a modern grid where batteries, wind, solar etc have destroyed that economic niche.
what you mean is likely "backup capacity". And yes heavily renewable grids will likely need some standin / backup generation for exceptional circumstances, for the foreseeable future. The economics and sizing of this backup is almost entirely unrelated to the economics and sizing of "base load generation". (for eg, there will never be a time when a diversified grid is at zero. The amount of backup needed is a function of how frequent these exceptional events are, the mix of your grid, and how much you're willing to pay backup generators to avoid load shedding in these situation)