The Devil could very well have beaten Rick and got his soul.
The Devil opened up a shop that gave away items which would ave a positive effect and a negative one, the purpose of this was stated to be that the Devil was trying to harvest the souls of the patrons through these items.
Never was it established that the negative effects of the items was a necessary component for the soul to be reaped from the person who had taken them, very possibly the Devil was still getting those souls eternally damned to Hell.
A clever trick of the Devil would be to move into the town Rick lived in, hire his granddaughter to draw the guy into his shop, and trust in his ego to help him claim the soul of just about every person in town, including the scientist himself.
Even if this wasn't the case, the Devil need only claim this was his intention to Rick after he had finished selling the items he removed the curses from and he'd have claimed a victory over Rick by breaking him with the belief that he had damned himself and so many others (which would be a wound upon his ego).
Then all the Devil had to do was move shop to the next town and begin again. It's also inconsistent that in this and other episodes Rick, who claims to be a nihilist that believes in nothing, has a problem with nazis and pet abusers. If he is truly above petty morality, he'd not be offended by a swastika-clad skinhead.
Furthermore, as someone who claims to hate authority he's pretty chummy with the president of his country, the USA, one of the most corrupt places in the world. He says he appreciates honesty, so why'd he be against a fascist takeover? To him all governments are fascist, but at least actual fascists are honest about their intentions.
I hate pseudo-nihilists who act like they don't have principles but then act exactly like they hold the same moral/political sensibilities as the prevailing culture from which their author hailed.
Like "this guy is such a cool dude he doesn't care about anything" until he actually has to take a stance where he disregards some topic that mainstream society would actually judge him for not agreeing upon.
That's not to say that a nihilist character cannot be against fascism or animal abuse, but he'd be opposed to these things on the basis of what he personally likes or dislikes, he would judge everything by what he feels about it and by no other standard.
Rick Sanchez isn't even a nihilist, that's what a lot of people miss about him, in the Devil episode one of the first things he does is confirm that objective Evil does indeed exist in his opinion. In another episode it's shown that he created a hybrid of Lincoln and Hitler to see how a combination of perfect Good and Evil would function as a single individual, so not only does he believe in objective moral standards for Good and Evil, but he can also identify what kinds of people would best embody these values.
It's not like it doesn't factor into the plot in a significant way, he frequently refers to Good and Evil in subtler ways as they inform his actions. To say he's a nihilist is to ignore the ample evidence to the contrary.
Rick is not philosophically inclined, he is in every way a reflection of his creators, I believe one video I watched said it best:"Rick Sanchez is a smart guy written by a dumb guy who thinks he is smart, but has no clue about what intelligent people are actually like".
Rick is a marty stu who was in many ways a reflection for how his creators wished they could be. Kind of like how all these anime protagonists are wish fulfillment for the nerdy and horny men who drew them.