There is a big difference between a vendor not doing business with google (or other US companies) and its devices not being able to use any services from google (or other US companies).
First, not having gapps (the google apps and google play services package) pre-installed doesn't mean customers/shops can't install it themselves. There is a thing called opengapps. In fact that's what people have been doing with 3rd party roms anyways, as those are not google certified.
Second, even if customers can't/don't know how/won't bother to install gapps, the only big thing they cannot use for sure is the play store. For other services, they can either:
- Install and use the specific app anyway. For example google maps and google keyboard are not google framework dependent, they can be installed and run on any modern android compatible system. Same goes with non-google platforms like facebook and twitter.
- Use web interface or many of the existing 3rd party clients to access the service (e.g. google drive, google calendar, gmail, youtube). For example I'm a gmail and google calendar user, but I never used the official gmail and google calendar apps, as I found 3rd party clients more fitting to my needs.
Will google implement checks to deny any Huawei devices from accessing the above services? Very unlikely because:
- As long as these services are accessible to 3rd party developers or on the web, it is technically unfeasible to block their usage on Huawei devices specifically.
- Google has agreed to continue provide service (including play store) to existing huawei phones, making it more difficult to single out future huawei phones. If they pull services from existing users it could lead to legal actions worldwide. Google is already having plenty of legal troubles in Europe, doing this would be like adding fuel to fire.
- The whole "ban huawei" thing is fundamentally against google's business interest. In the long run this will severely threaten its dominance in the smartphone ecosystem. It is unlikely that they'll try to do anything beyond what is absolutely required by US law.
- It is also unfeasible for the US administration to force US internet companies to actively check device origins and selectively block some of them, as this goes beyond the scope of export regulations and reaches the realm of cyber warfare.
In general, I think the effect of a google ban on huawei phones is way overblown on most media reports.