Is there any possibility to lock between policies ?

So, is the bucket locked ? Will the bucket not be deleted by normal means , especially, when the Bucket policy or the IAM policy given to the user) cannot be changed by a developer (who is not an admin) ?

If deletion is explicitly prohibited by the bucket policy, the IAM user cannot delete it.
For example, unless you specify a user who can be deleted using the "Condition" key as shown below, you will not be able to delete it.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Principal":"*",
      "Action": [
        "s3:DeleteBucket",
        "s3:PutBucketPolicy"
      ],
      "Resource": "arn:aws:s3:::s3-bucket-name",
      "Condition": {
        "StringNotEquals": {"aws:username": "admin"}
      }
    }
  ]
}