senior engineers are leaving in my team, is this a red flag?

I joined the company 8 months ago as SRE in UK. i got an mentor helping me to onboard to the team and I joined the team with lots of senior which i think i can learn a lot from them.

However, starting end of last year, my mentor resigned and got an offer to elsewhere. Then the other senior is also resigning. Both got a job offer and quit. I originally thought it is normal as they have been staying the company for 5 years. 

As two members left, it seems my team didnt get any backfill, and resources have been heavily invested in India. In terms of project wise, I am currently working a non critical project, later found out in all hands it is going to be decommissioned after 2 years. I asked my manager that I wanna to work on the organisation priorities project, but it seems my team have no ownership and my manager reassured me that if we have this opportunities in the future, he will put me into the project. in terms if performance review, i got an average rating (meeting expectation) now my team is left with 3 members and i felt like i do have any impactful projects, it is very hard to get exceeding expectation and also very scared to be put in piped. in this scenario, should i trust my gut feeling this team is shrinking and i should start to look for other job or it is a normal to get a non-critical project and I still be fine as long as my manager are happy with my performance?