If SCOTUS decided that Gonzales v. Raich abuses the commerce clause to ridiculous proportions and overturns it, would they necessarily have to overturn Wickard v. Filburn also?
First of all, SCOTUS never overturns cases because they think that a prior ruling was "too ridiculous." And, for what it is worth, Wickard is far more ridiculous in the face of the plain language of the constitution and reasonable inferences about what it means in light of modern conditions, than Gonzales v. Raich.
Secondly, it depends upon the actual reason that SCOTUS articulated for overturning Gonzales v. Raich, if it did so.
For example, it might hold that a statute which didn't exist at that time, or wasn't raised in that case, compelled a different result on the narrow question of whether states could legalize drugs notwithstanding the federal controlled substances act's provisions to the contrary. Or it could hold that Gonzales v. Raich should be overruled because the constitution created a constitutional right to use psychoactive drugs (as it has already done so narrowly in certain religious liberty cases involving the ritual use of peyote by Native Americans, where there was use of the drugs in question in religious rituals since prehistoric times). In those cases, which wouldn't hinge on the extent of the commerce clause power of Congress, Wickard v. Filburn wouldn't be implicated and would remain in full force and effect.
On the other hand, if the U.S. Supreme Court overruled Gonzales v Raich on the grounds that its commerce clause power holding in that case was overbroad and that it was unconstitutional for Congress to regulate the intrastate sale, distribution, consumption and possession of drugs, it is hard to see how the Wickard v. Filburn precedent could survive and the decision would probably expressly overrule Wickard as part of its reasoning.
But, honestly, given the makeup and recent rulings of the current U.S. Supreme Court, it would probably be more likely for the broad commerce clause power holding of Wickard v. Filburn to be overturned, which would cast doubt upon but not automatically overturn Gonzales v. Raich, than it would be for Gonzales v. Raich to be overruled on commerce clause grounds. Even without Wickard, SCOTUS could very well decide that the Controlled Substances Act is within the scope of the commerce clause power, even if SCOTUS agreed that Wickard itself (which found that growing food for personal consumption on a farm entirely located in one state could be regulated by the commerce clause) went too far.