Oracle Standby Database - Archivelog GAP Good Afternoon!

I've done some research around fixing archivelog gap between Primary and Standby databases, and a few links provide tips on the querying V$archived_log, v$archive_gap and v$log_history. They are really great source of information, however, I have a scenario in which both servers need to have archivelog retention due storage limits, so standby database let's say, has archivelog sequences from D to P, and from P to R, being R today's.

What would be the implications, apart from having missing data, in a case of need to put standby temporarily as production db in case of failure? Would it work, or the best practice is to recreate stdb database and apply only continuous archives from now on?

Thanks.
Assuming you mean that the database is "missing" logs from P->R, and that your primary database no longer has those logs either, then the answer is that you'll have a functional database (upon standby activation as a primary) but you will be missing data from P-> the Activation point. 

The thing to remember here is that your standby is only as good as your last archive log that was fully applied. Without intervention on your part, your standby database is essentially frozen in time, and will never advance.

If you're missing archive logs, and they are truly unrecoverable (did you check storage backups? Backups to tape?), then your standby, IMO, is worthless as a production level standby. You, and your business, may have a different opinion based on your usage of the database in question.

But if this was truly a production level standby database that is meant to take over for production in a disaster scenario, personally, I would rebuild the standby immediately.