Well, Mike, if his father said he would continue searching the river I would think that he himself doesn't think it impossible that Steven is in the river, deceased. After such a long time they have certainly entertained that possibility. My advice would be to approach him with an offer to help searching, or spreading awareness, anything he needs/suggests, and then take from there. You could ask him about the river searches he planned last year, the areas he's searched, did he go by boat or just walked the shoreline, etc, and bring up the islands then if he has not searched there yet. A helicopter might miss small items hidden in brush etc, foot and boat searches are certainly necessary. You could offer to go with him, or to reach out to professional search teams, if he hasn't done that yet. I think he will be grateful.