As far as I understand your certificate is still valid but you need to remove the intermediate certificate from your bundle. That was the case for me anyway.
If your traffic comes from a browser you are fine with this but if you're coming from e.g. Curl you will find that you need to include an intermediate chain.
(The reason for the difference being that browser stay up to date, many old client systems do not.)
We ended up getting a new cert from a different provider.
You only need to remove the cert if you want to support buggy clients. If none of your clients are buggy, it will be fine to leave the expired cert in the chain.
