Misscarage. This is missed abortion?

I'm 34yr. & my husband is 39. I have a 11 yr baby. In 2014 a misscarage than anthor have now again missed after fertility teartment. My lmp was 15/03/17.on10/04/17 i have spoting & chek by home pregnancy test which was positive. Next day doctor prefer beta hcg which is 598. This day u/s done but nothing detect. After 11days(22/04/17)U/s detect sac persent but no heart beat. Dr prescribed progesterone 300 mg(OD) & sildenafil 25mg (Tds). I have 3 tablets of sildenafil 75mg (by mistake) & 1 progesterone tablet taken at night(10 pm) . Next day at 6 pm I have seen brown spoting at my pantie.I am worried this due to overdose of sildenafil. I call to doctor but he said this not happened due to sildenafil. But I was stopped sildenafil after this. I have Continued progesterone. On 28/04//17 u/s detect no heart beat Dr says missed abortion. I have some questions 1 . is there still any hope. Means I can wait some days for coming heart beat? . 2.what is your opinion means this is missed abortion?