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.