One problem of Ghazni was its over-extension : what we have there is mostly the success of one man, Mahmud, over its neighbours due to his personnal skills. Even during his reign, he had to regularly fight back Turkic peoples and Central Asia khanates.
Giving that Samanids already began their fall since 999, I fear that Ghaznavids may have been taken between two fronts there.
Now, assuming they survive it, I don't think they could have done a great conquest up to the West :
- Divided structure : Harun ibn Altun, as his father before him, was independent de facto and his rebellion against Masud was more the formalization of the situation.
- Lack of "targets" : Ghaznavids owed their power to the regular raids they did in India, giving them wealth and prestige. What was left in India were quite more powerful kingdoms.
-Succession querells
Admitting they can smithe back Selkujs, I think they would have tried to crush whatever remained of Samanids and go against Buyids that supported their Persian vassals rebellions. Such would have probably provoked an influx of Sunni Turkic mameluk in the region, at it precisely lead to Ghaznavid appearance. I can see them crushing Buyids hard enough to provoke the fall of their hegemon on Abbassids themselves, but it doesn't mean that their presence would be much welcomed.
After all Khwarezmians weren't that much themselves.
With these issues, and still a growing Turkic presence in Iran, I don't think they would have made it to Baghdad, not mentioning Byzantium.