Either you don't understand me, or I don't understand you. Of course if the image layer is beneath the video, the video will play over it. But if the video is ended, the video vanishes and the image source becomes visible automatically. And if the image contains the last frame of the video, it looks as if the last frame of the video is displayed indefinitely.
If you have a text source to write text over the video, it will write over the image with the last frame as well.
Put the text source on top. The text is always visible, because it is on top of all.
Put the video source below the text source. As long as it is playing, it shows the video. It vanishes, as as it ended playing. The text from above is always written over it.
Put the image source with the frame below the video source. It is hidden by the video, as long as it is playing. If the video source vanishes (becomes transparent) at the end of the video, it becomes visible. The text is still written above all, so it appears as if the text is written over the last frame.