If Alphabet was to shutdown, other compaines would fill the void with their own products. Some will be existing companies, and some will be new companies.
There are lots of alternatives to many of Alphabet/Google's products but people don't know about them because Google dominates so many product spaces.
There are other email providers to Gmail. There are other map options too.
I can easily believe companies will create their own mobile OS to fill the absence of Android (Jolla already exists, maybe Windows Phone will make a comeback?!)
There are other search engines too. We have a variety of web browsers.
We'll still have all the free fonts previously hosted at fonts.google. Someone else will probably collect and host them in a central place or people might be more likely to self-host them.
GSuite can be replaced by alternatives (they already exist).
Of course, there is a lot of back-end engineering that Google has contributed to the internet infrastructure we don't see. But the web will continue to work fine.
Two Google products I can't see being easily replaced:
- Street View: this is something that needs the time and resources of a large company.
- YouTube: this has accumulated so much content it's hard to see this replicated easily.
So, yes - a lot of the user-facing products from Alphabet/Google can be provided by other companies, or can be created by other companies.