Existential Crises Have an End.
How would you deal with an indeterminate life?
What if you just continued to exist without end, watching everything you love disappear? Family, friends, trends, places, things. Everything is ephemeral, including you. But if you weren't, what purpose would your life serve? If you had no end? What meaning is there in existing indefinitely? Would you seize the day? Make every day count? Would you just exist without putting any effort in? Would you turn in circles asking yourself why you, what for, to what end if you have none? What would you look like, if you had an infinite amount of time to puzzle over the question you're asking yourself now?
For me, the situation didn't change. So what if I've got an infinite lifespan? The "Big Questions" are practically the same. When I look at how mind-boggling the universe is compared to me, how huge; how intricate; how minuscule the pieces are; and how (in)significant I am, it's easy to get lost in between. Then I'll take a deep breath, see the beauty of everyday mundanity, and remind myself: I don't need to go looking for the big picture. For me, I should be the big picture.
There is an ominous, unknown, and imagined cloud, which exists only in your mind. You may go about fearing it, and make the time before the actual storm more miserable. Alternatively, and possibly preferably, you can laugh, cry, and spend your time doing what's best for you and those around you. Not a purpose, just a mindset. And that's my big picture. My tapestry. The story I tell is guaranteed to end, be forgotten. But my decisions, I am bound to live with... for a lifetime. Until the end of my tapestry. Focus less on what is outside your tapestry, unless you like it. You can decide some of the things that enter your tapestry, if you are conscious and purposeful about obtaining it.
Perhaps a more practical answer is: When you are doing something, do it. Reserve your focus for what you want to focus on.
You have a finite amount of time in front of you, right now. Question for question, what are you going to do with that time?