Airtel pre-paid - Roaming internationally and keeping SIM card alive

Hello Airtel experts - I have an active Airtel pre-paid SIM card (purchased in India 2016). Currently, I am in Europe for a short term assignment (2-3 years). Is there a way to keep the SIM card alive while I am here in Europe? I understand that regular re-charge will help (and keeping a minimum balance), but is there any definitive answer on what the minimum requirements are to keep the SIM alive? I keep getting messages from Airtel asking me to upgrade to a 'roaming plan', but I don't really use this SIM (I have a local European SIM - much cheaper). Roaming plans costs are high and some are valid for only 28 days. I just want to keep the Airtel SIM alive for the next 18-24 months. I had asked this questions a few years back, but wondering if there is any update on the issue. Thanks!

Not sure, if this is useful for you now. Probably, useful for others with the same question. My cousin lives in Abu Dhabi, stays there 10 to 11 months a year and comes to India only for 1 or 2 months. In order to retain his number I recharge with 446 that comes with 90 days validity. It has been working fine during the past 15 months (including a month of stay in India). 446 includes a few countries in Europe too, but not all counties from EU. Anyone can checkout the list of countries at Online Mobile Recharge, Prepaid Mobile Recharge - Airtel . I hope that helps.