I think you don't understand the concept and expenses of ABM. It's very expensive and it takes decade to develop such technology. China is developing her ABM which will be operational by 2020. We are also developing 2 Layer of quality ABM. AAD/PDV- 2,000KM (2014) and AD-1,2 - 5,000 KM (2016). Everything going as per schedule and we started the development some 6-7 years back.
Also, US has offered Patriot System, Russia has offered S-400/500 (we already have S-300). We can also Buy Arrow-3 from Israel. We will be operating our ABM which will be world class. If it won't serve the purpose or fail for any reason (which i don't know as of now), We can always Buy any of the 3 best ABM from US, Russia and Israel. These systems won't be sold to any other country. In Short, We will have best ABM in future even if our fails (chance is negligible). China is far behind and long way to go. Pakistan can't buy from Russia, Israel, US nor it can develop on own. So, Only hope on China that also after 10 years minimum (that also If China makes something good and imports to Pakistan which also no one can confirm). A very hypothetical situation.
Thank you maybe I dont but it looks very much like an escalation of an arms race which idont approve of. anyway if it takes decades it will probably take more time for india cos indian procurement seems somewhat a slow process