I'm consuming a soap service from a server that uses ssl certificate. Although I don't have any dependency on the server certificate in my code, but what if the server certificate gets expired? Will the communication between the server and my client be OK?
In general: no, the communication will not be OK.
A certificate is an endorsement, by the issuer, that the requester has met the identity (and other) requirements that the issuer has put in place; and that the public key in the certificate really is associated with the subject.
The expiration date for the certificate exists because the longer ago the verification process was, the more likely it won't hold up anymore. Imagine you bought awesomesauce.example.com, and got a TLS server certificate for it, and the cert had no expiration. After a year you forget to pay your registrar and lose the name. Someone else comes along, buys it, and has a popular website there. You realize that you have a certificate that identifies you as that site, so you sell it for a million BTC to some hacker group who uses it to do various identity theft tricks and ...
This is similar to an expiration on a driver's license. Maybe your eyesight has dropped below the acceptable thresholds and you shouldn't drive. Maybe you moved and the address on the card should no longer be trusted. Slap an expiration date on there and you now have to reaffirm the facts therein.
You can get an idea of how your client will handle expiration by making a request to https://expired.badssl.com/. If it works, you're trusting outdated claims. If it doesn't: be happy about your client doing the right thing.