As you said yourself there are many grey areas here. I will wait for SC judgement on this issue before coming to any conclusionsSC has not defined what Basic Structure means.
parliament can as per power under Article 368 amend any part of the Constitution. Our founding fathers of the constitution said the power of parliament to amend the constitution is unlimited as The Parliament takes up the power of the constituent assembly when amending the constitution.
Thats what 42nd Amendment by Indira Govt in 1975 during Emergency survived the SC preview.