Searching Magus here gives the relevant errata for the remaster;
https://paizo.com/pathfinder/faq
If you use a spell that requires a spell attack roll like Gouging Claw and miss then you lose the spell.
If you use a spell that requires a saving throw like Enfeeble and miss they avoid the strike, but are still affected by the spell. If you critically miss then the strike misses and they are not affected by the spell. You lose the spell in that case. The enemy still rolls a fortitude save like normal in order to determine the effect of the spell.
As a Magus you're still going to want to focus on attacks that use spell attack rolls with spell strike. You'll have better accuracy with them. With save based spells the main benefit of spell strike is that you're doing in two actions something that would require three actions if you used each part separately.