Is there a standard way to find out if my bridge or ip is tainted/blocked and therefor no longer relevant (and I better run a relay)?
There is not really one single public “tainted” flag for a bridge, because being easy to enumerate would defeat part of the purpose. I’d look at practical signals instead: is the bridge getting users/traffic in Metrics, did reachability tests start failing, and do users in the censored region still connect through it? If it stays reachable but has no use for a long time, then switching to a relay may be more useful, but I would not assume one blocklist result means the bridge is worthless everywhere.
No. As in general censors are blocking obfs4 bridges by IP, you can check if your bridge IP is blocked in some regions:
itdog.cn supports TCP ping too: https://www.itdog.cn/tcping or https://www.itdog.cn/tcping_ipv6/