If your player is an HDCD-capable player, it will decide the upsampling question for you because it is a licensing issue. The player will either leave the decoded HDCD at 44.1 khz, or it will upsample it using PMI's upconversion filters.
If the player is not an HDCD-capable player, it will upsample with its standard upsampling algorithm but will not decode the HDCD, i.e. it treats HDCD as standard redbook.
If the player is not an HDCD-capable player, it will upsample with its standard upsampling algorithm but will not decode the HDCD, i.e. it treats HDCD as standard redbook.