In some cases, we find one Fallopian tube is Open in HSG and another tube is blocked in HSG. What to do in that case?
Please remember, one Fallopian tube can be sufficient for pregnancy. So, you DO NOT need any Laparoscopy or IVF if all other factors are normal.

If one tube is blocked and other is open, do I need Laparoscopy?
In this case, laparoscopy is needed ONLY in the following circumstances-

1) If any tube is swollen (Hydrosalpinx), because the fluid inside the Hydrosalpinx can damage the embryo. In that case, even if you need IVF, the hydrosalpinx MUST be removed by laparoscopy.

2) If you need laparoscopy for other reasons like Severe pain during periods, Ovarian Cyst, Endometriosis, Fibroid. In these cases, laparoscopy is needed to remove these diseases and improve your chance of pregnancy.

If only oneFallopian tube is open and other is closed, can I try naturally?
Of course, you can try. Even you can have Ovulation Induction (OI), by which medicine is given to improve your chance of pregnancy. However, for how long you will continue this type of treatment, depends on your age, duration of trying for pregnancy, condition of your husband's sperms and your ovaries. If any of these are not satisfactory, you should not rely on trying "naturally" for long periods.

If one tube is blocked and another tube is open, can I try IUI?
In most of cases, if your ovaries and your husband's sperms are good and your age is relatively young, you can try IUI. In most cases, the results of IUI is good. However, in some specific tube block, IUI result is not satisfactory.

Do I need IVF if one Fallopian tube is open?
You need IVF only if your husband's sperm condition is not good, your ovaries are not functioning well, you have been trying for pregnancy for long time or your age is on the higher side. If IUI fails, in that case, also you need to think about IVF.

Conclusion
In majority of the cases of one Fallopian tube block (and other tube remaining open), you don't need to worry. There is no need for laparoscopy or IVF if all other factors remain satisfactory.