Enthuware

I bought voucher for 6 months (2 months ago) for Java SE 11 Programmer I. I wanted to take the exam in the middle of October.
But there is new information about new type of exam. Java SE 11 Programmer I | 1Z0-815 will be replaced by 1Z0-819 on October 1st 2020.
I have few questions:
1. There is no more two parts ( SE I & SE II) of this java certification?
If yes, do I need to have knowledge from both dedicated books ( part I and part II ) ?
2. What about my voucher? It will change by itself for new exam voucher?
If yes, will I have next 6 months to take the exam or my expiration date will be the same as now?

1. Correct. There will be only 1 exam 1z0-819 from 1st Oct 2020. Yes, it will require you to know the topics discussed in both the books.
2. No, voucher will not change itself. It will expire as scheduled. You have three options - ask oracle to extend the expiry, schedule 819 exam using the same voucher before it expires, or sell the voucher to someone who is taking some other certification exam such as OCA/OCP Java 8, or 1z0-900. You may have to sell it at a discount but at lease you will not lose it completely.

What if I will take the exam before 1 October and I will pass. After that I need to pass 819 anyway to get whole OCP cerification or I have to take the 816(which will expire on 1 Oct. too?

After 1st Oct, 815 and 816 will not be there. Only 817 and 819 will be there. So, if you have passed 815 before Oct 1, it wouldn't matter. You would still need to take 819 to get OCP 11. If you passed OCP 8, you can take 817.